If Salvation is By Faith, Why Did God Give the Law Through Moses?
Sunday, December 13, 2009 -
Galatians 3:15-18 - “To give a human example, brothers: even with a man-made covenant, no one annuls it or adds to it once it has been ratified.  Now the promises were made to Abraham and to his offspring. It does not say, "And to offsprings," referring to many, but referring to one, "And to your offspring," who is Christ.  This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void.  For if the inheritance comes by the law, it no longer comes by promise; but God gave it to Abraham by a promise.”
1) GOD HAD NOT ANNULLED THE TERMS OF THE COVENANT WITH ABRAHAM BY THE GIVING OF THE LAW 430 YEARS LATER - Galatians 3:15 & 17 - “To give a human example, brothers: even with a man-made covenant, no one annuls it or adds to it once it has been ratified....17....This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void.”
Paul uses this illustration of a legal, binding agreement, perhaps something like a will, to prove his point. Just as a will can’t be altered after the person has died, so the giving of the law to Moses didn’t alter the covenant made with Abraham basing righteousness on faith rather than works - see Galatians 3:6 - "....just as Abraham "believed God, and it was counted to him as righteousness"
2) THE TERMS OF THE COVENANT GOD ESTABLISHED WITH ABRAHAM AND THE COVENANT GOD ESTABLISHED WITH MOSES ON SINAI WERE THE SAME TERMS - FAITH AND ITS LIVING EXPRESSION OF FRUITFUL OBEDIENCE
It has been eternally true that “....without faith it is impossible to please God” (Hebrews 11:6). God has always and only responded to faith. But this faith must be more than merely the initial act of faith. Faith must be the ongoing life-style of all who would follow Him and live for Him. This ongoing nature of obedience in genuine faith is why the law was given to Moses. The law was given to do two things:
a) First, the law was given to show what a life of faith looked like when expressed within the theocracy of Israel. That last phrase is particularly important. The Old Testament law was a manifestation of theocratic law.
b) Second, the law was given to reveal to people their unseen tendency to use the law, not as an expression of living faith, but as a tool of proud, self-reliant religious merit before God. In other words, we need the law to expose human pride.
This, of course, is the very sin Paul had to come to terms with in his own religious devotion - Philippians 3:7-9 - “But whatever gain I had, I counted as loss for the sake of Christ.  Indeed, I count everything as loss because of the surpassing worth of knowing Christ Jesus my Lord. For his sake I have suffered the loss of all things and count them as rubbish, in order that I may gain Christ  and be found in him, not having a righteousness of my own that comes from the law, but that which comes through faith in Christ, the righteousness from God that depends on faith....”This was also the very sin Paul said Israel herself needed to come to terms with and repent of - Romans 9:31-33 - “....but that Israel who pursued a law that would lead to righteousness did not succeed in reaching that law.  Why? Because they did not pursue it by faith, but as if it were based on works. They have stumbled over the stumbling stone,  as it is written, ‘Behold, I am laying in Zion a stone of stumbling, and a rock of offense; and whoever believes in him will not be put to shame.’”
3) WE, IN THE NEW TESTAMENT CHURCH, NEED BOTH THE EXAMPLE OF THE COVENANT OF FAITH WITH ABRAHAM AND THE EXPRESSION OF FAITH IN THE COVENANT ON SINAI
In fact, each of the key players in these two covenants explained the nature of their covenant in terms of the other: Genesis 22:16-18 - “By myself I have sworn, declares the Lord, because you have done this and have not withheld your son, your only son,  I will surely bless you, and I will surely multiply your offspring as the stars of heaven and as the sand that is on the seashore. And your offspring shall possess the gate of his enemies,  and in your offspring shall all the nations of the earth be blessed, because you have obeyed my voice."
Notice how God speaks to Abraham, upon his willingness to offer his son Isaac, in terms of the original covenant he made when he was first called. Later, God would speak to Isaac in the very same covenantal terms - see Genesis 26:4-5 - “I will multiply your offspring as the stars of heaven and will give to your offspring all these lands. And in your offspring all the nations of the earth shall be blessed,  because Abraham obeyed my voice and kept my charge, my commandments, my statutes, and my laws."
Also, notice how Moses describes the terms of the covenant made on Sinai in the very same terms of grace that God initially made with Abraham. The very same words are used - Deuteronomy 7:12-13 - “And because you listen to these rules and keep and do them, the Lord your God will keep with you the covenant and the steadfast love that he swore to your fathers.  He will love you, bless you, and multiply you. He will also bless the fruit of your womb and the fruit of your ground, your grain and your wine and your oil, the increase of your herds and the young of your flock, in the land that he swore to your fathers to give you.”
4) THE CHIEF OBJECT OF BOTH OUR FAITH AND OBEDIENCE IS FATHER GOD’S PERFECT REVELATION IN JESUS CHRIST - Galatians 3:16 - “Now the promises were made to Abraham and to his offspring. It does not say, "And to offsprings," referring to many, but referring to one, "And to your offspring," who is Christ.”
There are four ways in which Jesus Christ qualifies as the promised seed of Abraham:
a) Jesus was a Jew in the strict physical sense. He could trace his lineage back through David, to Abraham.
b) Jesus lived a life of faith, which, in terms of Galatians 3:7 is the ultimate manifestation of being truly a descendant of Abraham - “Know then that it is those of faith who are the sons of Abraham.”
c) Christ’s death and resurrection accomplished the righteousness that Abraham had “reckoned” to him by faith - Galatians 3:8 - “And the Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand to Abraham, saying, "In you shall all the nations be blessed."
d) Only by belonging to Christ through faith (like Abraham’s living, obedient trust) can we become true children of Abraham and inherit the blessing of justification - Galatians 3:29 - “And if you are Christ's, then you are Abraham's offspring, heirs according to promise.”