Now that he has established that Abraham was justified by faith and that the true heirs of Abraham are those who believe as he did, Paul now turns to the Law’s effect on God’s promise to Abraham (all nations shall be blessed in you) and the Law’s purpose.  He anticipates the false teachers’ response to his argument about Abraham’s justification.  One objection will be that the Law came after the promise to Abraham and thus changes its terms.  If the Law is the most recent word of God it is logical to assume that it is the standard.  Second – if Paul argues that the Law has no place in justification, then why did God give it to Moses?  Has not Paul made the Law unnecessary with his claim that justification is by faith alone?  And if that is the case – is Paul saying the words of God to Moses have no purpose?

Paul uses these verses to paint a picture of Israel’s history from Abraham to Moses to Christ and show that God’s plan of salvation was always consistent and has never changed.  An unchanging God does not adjust His ways and a faithful God cannot amend His promises.  The promise to Abraham is still valid and the Mosaic Law has purpose – and neither one contradicts the other.

Does the Law Change the Promise? (15-18)
In verse 15 Paul uses an illustration to make the point that the Law did not change the covenant God made with Abraham.  He says even a human covenant (can also be translated “will”) cannot be changed after it is ratified.  Perhaps a better way of understanding his point – since in our time contracts can be amended – is to say that a will cannot be changed after the death of the one who made it.  He completes the point in verse 17.  The Law – which came 430 years later – did not change God’s covenant with Abraham which was based on faith.  If a human covenant cannot be changed after it is ratified, how much more does God’s covenant remain the same regardless of circumstances or time?

Paul’s reference to 430 years is interesting.  It is the number of years the Israelites were in Egypt per Exodus 12:40.  If 430 is correct for the time in Egypt, then the years between the promise to Abraham and Sinai were certainly more than that.  It could be that Paul simply uses a recognized number to show that the Law was long after the promise.  Or his reference could be to the time from when the promise was confirmed to Jacob (Gen 28:14) to the Law at Sinai.  Regardless of the exact meaning, Paul’s point is that the Law came long after the promise and does not establish a new basis of belief that contradicts it.

Paul says the promises (plural – probably means all that God promised in Genesis 12 regarding Canaan, making a great nation, and the Messiah) were to Abraham and his seed.  The word for seed is singular rather than plural, which means it refers to One Person and not many.  He does not mean the word seed cannot refer to many people – since it clearly can and often does.  He means the author of Genesis intended for it to mean one special descendant – that is, Christ.  His point is that the only way the nations could be blessed through Abraham’s seed was for the seed to refer to something other than all of his descendants.  The world would not be blessed through Israel becoming great and possessing the Promised Land.  The world could only be blessed through ONE – the Messiah.

In verse 18 he summarizes this section on law versus promise.  The inheritance – justification – was granted to Abraham based on a promise (note the number of times Paul uses the word promise in these eight verses).  God simply told Abraham He would bless the world through his seed; He did not make it contingent on obedience.  If the inheritance was based on promise, it could not have been based on the Law and vice versa – they are mutually exclusive (2:21).  Since he has already shown it was based on promise, by definition it was not based on the Law.  So God is and always has been consistent.  Abraham was justified by faith and everyone who has ever been justified – before or after the Law – was justified by faith also.

This means the Galatians are going down the wrong path.  They and the false teachers both want the inheritance of Abraham, but the only way to attain it is to do it the same way he did – through faith.  This restates what Paul said in 3:7-9; the true sons of Abraham (heirs to his inheritance) are those who believe as he did.

What is interesting is to compare Paul’s words here with three examples in Genesis that seem to emphasize obedience.  In Genesis 18:19, God says He chose Abraham so that he may command his children and his household after him to keep the way of the Lord by doing righteousness and justice.  In 22:16-18, God repeats the promises to Abraham regarding his descendants becoming a great nation and the world being blessed through his seed and says it is because of his willingness to sacrifice Isaac in obedience to God (see also Jas 2:21).  In 26:4-5, God again repeats the promises, but this time says them to Isaac and says they are based on Abraham’s obedience in keeping My charge, My commandments, My statutes and My laws.  In one sense these verses could be used to back the false teachers’ claim that Abraham’s justification was based on obedience instead of belief.  But comparing them to Paul’s words and understanding Genesis 15:6 – belief reckoned to Abraham as righteousness – means obedience is the EVIDENCE of belief rather than the basis for it.  God chose Abraham (18:19) and Abraham believed and was justified – and as proof of that belief he obeyed God.  God blessed his obedience because it was a sign of his justification.

Throughout the Bible obedience is always shown the same way.  In terms of the Mosaic covenant, God told Israel the blessings of the covenant were contingent on obedience – Deut 7:12-13, 8:18, 30:15-20 – but the covenant itself was based on Him – Deut 4:31.  The same is true today.  Jesus said those who love Him keep His commandments – Jn 14:15-24 – but John said we only love God because He first loved us – I Jn 4:19.  Several New Testament writers show that obedience is proof of belief and without obedience there is no evidence of justification – Jas 2:14-26, I Jn 1:6-7, 2:3-6 – but obedience is never the basis of justification – Rom 10:8-13.

Does the Law Have a Purpose? (19-20)
Verse 19 opens with a logical question based on Paul’s obliteration of the Law as a basis of justification.  Why the Law then?  “Paul, you say the Law does not justify and it does not change anything promised to Abraham and it came hundreds of years after the original promise to Abraham – so what was the point of God giving it to Moses?  If it is worthless, why did God go to such great lengths to make sure His people had it?” 

Paul answers his own question directly and succinctly – it was added because of transgressions.  The purpose of the Law was to show man to be sinful (Rom 3:20, 4:15, 7:7-13); to show him the standard by which he is ultimately judged.  The Law marked clearly the gulf between man and God (but did nothing to bridge the gulf).  The Law showed the vanity of pursuing justification through man’s effort.

He goes on to say the Law was ordained through angels by the agency of a mediator.  That the Law came through angels is according to orthodox Jewish beliefs.  Stephen referred to this when he spoke in front of the Jewish religious leaders before he was stoned (Acts 7:53).  The author of Hebrews also refers to it (2:2).  The mediator is almost certainly Moses.  God did not give the Law directly to the people – He used angels and Moses.

He says it was added until the seed should come to whom the promise had been made.  The Law’s purpose was to show people how sinful they were and point them to the only solution to their sin – the promised seed.  It was not meant to be a permanent basis of salvation; it was to make people see their need and seek to meet that need outside of it.

Verse 20 is very difficult to understand and has a myriad of interpretations from different commentators.  What Paul could be saying is that the original promise is superior to the Law because it was spoken directly to Abraham rather than through intermediaries as the Law was (through angels and Moses).  He also could mean that the same God (God is one) gave the promise to Abraham and the Law to Moses so the two cannot contradict each other (although this does not address what is meant by the first half of the verse). 

John Piper’s exposition of this verse is as follows: I am not going to deal with this because I don’t know what it means. I cannot figure out how the two halves of verse 20 relate to each other. I would be happy for anyone to give me insight here.

Does the Law Contradict the Promise? (21-22)
In verse 21 he continues on to the second question his argument against the Law could bring up.  Is the Law then contrary to the promises of God?  And he answers emphatically, “May it never be!”  In the rest of this verse he gives the negative reason why it does not contradict the promise and in verse 22 he gives the positive reason.  In this verse he says if the Law was able to impart life then justification would be based on it and it would be contrary to the promise (this is similar to vs. 18).  But the Law only establishes the standard; it does not enable anyone to meet the standard.  Thus it cannot give life and cannot justify and does not contradict the promise (and the same God gave both and God is one). 

Verse 22 completes the answer.  The Scripture (the Law) not only does not give life, it shuts up all men under sin.  The Law makes man understand his sin and the hopelessness of overcoming his sin.  It makes him understand that he is imprisoned in his sin.  Why does it do this?  So that the promise by faith in Jesus Christ might be given to those who believe.  It shuts up men under sin that they may believe in Jesus Christ and be justified.  The Law does not contradict the promise because its whole purpose is to point people to it. 

Consider: This makes the Law an act of grace.  God gave the Law ultimately to point us to Christ.  Without the Law we do not see our need.  With the Law the promise is given to those who have faith in Christ.

Note the words in the second half of verse 22.  What is given to believers?  The promise – it is God’s promise based on God’s will.  How do believers get it?  They do not get it at all, it is given to them.  What do they do to merit this receipt?  They do not DO anything, they believe.  What do they believe?  It is by faith in Jesus Christ.  Paul summarizes the gospel in one short sentence.  It is the promise of God (the promise is Jesus coming to earth to die) given to those who have faith in Jesus Christ.  Justification is based on Christ’s work and given to those who believe in Him.

Thought: Verse 22 shows there is no salvation apart from the knowledge of sin.  No one believes and receives the promise by faith in Jesus Christ without being conscious of sin.  We do the unsaved a disservice when we do not make them aware of the perfection and holiness of God and their complete inability to approach Him because of their sin.  Sin is the key to understanding the gospel.  Without sin there is no need of salvation.

Not until the Law has bruised and smitten us will we admit our need of the gospel to bind up our wounds.  Not until the Law has arrested and imprisoned us will we pine for Christ to set us free.  Not until the Law has condemned and killed us will we call upon Christ for justification and life.  Not until the Law has driven us to despair of ourselves will we ever believe in Jesus.  Not until the Law has humbled us even to hell will we turn to the gospel to raise us to heaven.  – John Stott

Summary
In these verses Paul gives the grand scope of God’s plan of salvation from Abraham to Moses to Christ.  Beginning in Ur and ending at Calvary, God’s plan never changed and never wavered.  He made the promise to Abraham that through his seed all the world would be blessed.  He gave the Law to Moses to show the world their need of that blessing.  And He sent His Son to fulfill the promise and provide the blessing.  The message from beginning to end is the same – salvation by grace through faith based solely on the work of Christ.

Thoughts
This text should make us rejoice in God’s faithfulness and grace. 

• God is fully faithful.  The Messiah was first promised to Adam and Eve in the garden immediately after they sinned (Gen 3:15).  Thousands of years later – after making a nation of Abraham to provide a line for the Messiah – God fulfilled the promise through the death of His Son.  God is ever faithful to His promises and cannot violate His word.  Regardless of our circumstances or actions or the passage of time, God is fully faithful and always true. 

• God is fully gracious.  He did not leave us alone in our sin.  He did not leave us ignorant and doomed.  When He gave the Law to Moses it was an act of grace to make us aware of our need for salvation.  And in grace He then provided that salvation through His Son and now gives us the grace to believe and live for Him.  It is by grace that we are saved and it is grace that sets us free from the law of sin and death (Rom 8:2).  And the Law came in that the transgression might increase; but where sin increased, grace abounded all the more, that, as sin reigned in death, even so grace might reign through righteousness to eternal life through Jesus Christ our Lord (Rom 5:20-21).

This text should also make us rejoice in the unity of the Bible.  From the first page to the last, the message is one.  Man sins, God saves.  The Bible’s message does not change from book to book or age to age.   God created for His glory and saves for His glory and acts for His glory.  And man benefits in each case.  The Bible is God’s revealed will and since it is the word of an unchanging God it is unified from start to finish.  We serve a faithful God who was merciful enough to give us His consistent word so that we can know Him and enjoy Him and glorify Him.