If you belong to Christ, then you are Abraham's seed, and heirs according to the promise (Gal 3:29).

Now you, brothers, like Isaac, are children of promise (4:28).

If you are in Christ, you are a child of God and an heir according to God’s promise. These two scriptures teach us that by promise we have become heirs of God, and by promise we live as children of God. God’s word promises about the rights and privileges given to the children of God. In order to enjoy these rights and privileges in your life, you will need to live by believing and trusting what God promises in his word.

The opposite of to live by promise is to live by the works of the law.

For we maintain that a man is justified by faith apart from observing the law (literally, without works of the law) (Rom 3:28).

The law is the standard set to show how righteous people should live on earth, and everything the law says is good. But when you try to keep it thinking you can, you will find yourself not keeping it. It is the pitfall that Adam and Eve fell into by eating from the tree of the knowledge of good and evil. Humans were created to live by God’s grace, not by their works. The law is good, but the human effort to keep it works against God’s grace.

It is through Jesus that we have become heirs of God. The heirs of God rule over the world spiritually as God created man originally in his image and let him rule over the word.

It was not through law that Abraham and his offspring received the promise that he would be heir of the world, but through the righteousness that comes by faith (Rom 4:13).

The “righteousness that comes by faith” refers to the kind of righteousness that was credited to Abraham when he counted the stars in Gen 15. He became an heir of God through this righteousness. It was before the law was given through Moses, and even before he was circumcised. It figuratively points to the fact that we, without keeping the law—by his grace, have become the righteousness of God through Jesus Christ.

God made him who had no sin to be sin [21] for us, so that in him we might become the righteousness of God (2 Cor 5:21).

It was not by our effort that we have become “the righteousness of God.” No man has become man by working hard to be man. If you, having been born to be man, are still trying to be man, you are crazy. If you are in Christ, you have become the righteousness of God by having been born-again, and you cannot be less or even more righteous than that. It does not depend upon, and has nothing to do with your works. In the same way, anyone who belongs to Christ, he/she is an heir of God by promise, and is entitled to all the rights and privileges given to God’s children. Jesus said:

Look at the birds of the air; they do not sow or reap or store away in barns, and yet your heavenly Father feeds them. Are you not much more valuable than they (Mat 6:26)?

Note that Jesus calls God as “your heavenly Father.” God is not simply God for you. He is your Father, and you are his child. And if you are his child, all the blessings and rights that he promises are automatically yours. Why do you still need to try to meet your own needs as if you were a slave, or one of his employees? The blessings God promises for us are gifts, not pay for our works. We live by promise under God’s grace.