Galatians 4:27-31

For it is written, Rejoice, [thou] barren that bearest not; break forth and cry, thou that travailest not: for the desolate hath many more children than she which hath an husband. Now we, brethren, as Isaac was, are the children of promise. But as then he that was born after the flesh persecuted him [that was born] after the Spirit, even so it is now. Nevertheless what saith the scripture? Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the freewoman. So then, brethren, we are not children of the bondwoman, but of the free. [Gal 4:27-31]

The story of the Nation of Israel is one that is of “children according to the promise”. Isaac, by whom the seed of Abraham was called, was a child of impossibility by human standards, but with God nothing is impossible. The greater promised seed was also a child of impossibility, but she that knew not a man conceived by the Holy Spirit and brought forth the Savior. In between there were others. Paul quotes here from Isaiah 54:1, where the prophet is speaking the LORD’s words about the Nation forsaken and then gathered by her Husband and Redeemer, the Holy One of Israel. And so we learn from this that the works which God completes that are impossible by human effort are more than possible with God. That which He promises He will perform. The one born of the promise will come forth, and the promise of God to complete His work in us will happen. He will perfect us, but it will not be by the flesh. (Gal 3:3)

When Paul here speaks of the one born after the flesh persecuting him that was born after the Spirit, he was probably speaking of this episode:

And the child grew, and was weaned: and Abraham made a great feast the [same] day that Isaac was weaned. And Sarah saw the son of Hagar the Egyptian, which she had born unto Abraham, mocking. Wherefore she said unto Abraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, [even] with Isaac. And the thing was very grievous in Abraham’s sight because of his son. And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be called. [Gen 21:8-12]

In the passage in Genesis, Ishmael is said to be mocking. In Galatians, it is said that he persecuted Isaac. It is quite possible that there was much more straining their relationship that this one episode of mocking. It is also true to say that the nations of the world in general, and oftentimes particularly those from Ishmael, are enemies of Israel, the Nation born to the seed of promise. In this case though, the enmity is from those who are after the flesh. In context of Galatians, it is those who attempt and press others to attempt to perfect the flesh according to law. Even today, there is a tendency to lean toward the reintroduction of law so that the Christian knows how to live. We who believe the scripture that we are not under law but under grace are accused of “easy believism” or of teaching “cheap grace”. But we do not teach any such thing. They attempt to “harmonize the law and the Gospel”, but law and grace are not in harmony. They are not the same song.

Now we know that what things soever the law saith, it saith to them who are under the law: that every mouth may be stopped, and all the world may become guilty before God. [Rom 3:19]

For sin shall not have dominion over you: for ye are not under the law, but under grace. [Rom 6:14]

The difference between living by the Spirit rather than by the flesh in regards to sin is stated in the following:

For they that are after the flesh do mind the things of the flesh; but they that are after the Spirit the things of the Spirit. For to be carnally minded [is] death; but to be spiritually minded [is] life and peace. Because the carnal mind [is] enmity against God: for it is not subject to the law of God, neither indeed can be. So then they that are in the flesh cannot please God. But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of His. And if Christ [be] in you, the body [is] dead because of sin; but the Spirit [is] life because of righteousness. But if the Spirit of Him that raised up Jesus from the dead dwell in you, He that raised up Christ from the dead shall also quicken your mortal bodies by His Spirit that dwelleth in you.

Therefore, brethren, we are debtors, not to the flesh, to live after the flesh. For if ye live after the flesh, ye shall die: but if ye through the Spirit do mortify the deeds of the body, ye shall live. [Rom 8:5-13]

In Galatians, Paul speaks of living by the flesh in regards to attempting to perfect ourselves by the flesh. Both cases are living by the flesh as opposed to living by the Spirit, and there is little difference in the language that he uses. All of us find ourselves at one point of life or another, even when we know better, giving the “bondwoman and her son” residence.

Nevertheless what saith the scripture? Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the freewoman. So then, brethren, we are not children of the bondwoman, but of the free.

Nothing that we accomplish according to the flesh has any inheritance or value with God. It is in that category of “wood, hay, and stubble” (1Cor 3:12). See the comparison between the ministry of the law compared to the ministry of the Spirit.

[Forasmuch as ye are] manifestly declared to be the epistle of Christ ministered by us, written not with ink, but with the Spirit of the living God; not in tables of stone, but in fleshy tables of the heart. … Who also hath made us able ministers of the new testament; not of the letter, but of the Spirit: for the letter killeth, but the Spirit giveth life. But if the ministration of death, written [and] engraven in stones, was glorious, so that the children of Israel could not stedfastly behold the face of Moses for the glory of his countenance; which [glory] was to be done away: … For if the ministration of condemnation [be] glory, much more doth the ministration of righteousness exceed in glory. For even that which was made glorious had no glory in this respect, by reason of the glory that excelleth. For if that which is done away [was] glorious, much more that which remaineth [is] glorious. [2Co 3:3, 6-7, 9-11]

Why would we not leave behind all attempts to perfect the flesh (Adam, who all in him die), or living to gratification of the flesh, and live by the Spirit? Since we are not children of the bondwoman, but of the free: