Gal 3:12 says “And the law is not of faith: but, The man that doeth them shall live in them.”
The principle of righteousness is a faith principle. It is a promise to be received by faith, and not a work to be carried out by efforts. God’s word of righteousness was that through Abraham’s seed, all nations would be blessed. It was a promise. Abraham believed it and was declared righteous. That’s how righteousness works- God does the work and you believe.
Bearing this in mind will make you understand that the law cannot bestow righteousness. Paul explains why in today’s text: “And the law is not of faith…”. Under the law, you have to work for the reward. “The man that doeth them shall live in them.” If you choose to live under the law, eternal life would then be expected as a reward for work, and not as a gift you simply believe to receive. Thus, the reward ceases to be a promise.
But God’s plan for righteousness and eternal life for man was by grace in Christ. It says: “For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life” (John 3:16). What people try to work for under the law, and fail woefully to achieve, you receive in Christ by believing.
Abraham’s faith set precedence for ours. Let’s learn from it: “For if Abraham were justified by works, he hath whereof to glory…”(Romans 4:2). In other words, If Abraham was righteous because of anything he did, righteousness ceases to be a promise fulfilled but a reward for his work. Read on: “For what saith the scripture? Abraham believed God, and it was counted unto him for righteousness. Now to him that worketh is the reward not reckoned of grace, but of debt. But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness” (Romans 4:3-5). The only way God gets the credit He deserves for our righteousness, is if we recognize righteousness for what it is- a work He did and that we must simply believe.