That is, They which are the children of the flesh, these are not the children of God…
The word was originally employed to denote what was by way of consecration put up in a temple. The "anathema" might be an offering of gratitude for deliverance or some other blessing; or it might be, in the ages of spiritual darkness, a kind of sacred bribe presented to the deity. But whatever it was it would, if of convenient shape and bulk, be hung up on a pillar, or suspended on the wall of the shrine. It thenceforward belonged to the god, and it would have been not only theft but sacrilege for any one, even a priest, to have appropriated it. When the term was adopted by the Greek-speaking Hebrews it was used in exchange for the Hebrew cherem, which had for its radical import the idea of severance. Whatever was by Divine arrangement utterly "cut off" from any man's enjoyment was cherem to that man. God reserved its use. It was His cherem. If it were a thing that still continued fit for human use, God might assign it to His peculiar servants for their benefit (Leviticus 27:21; Numbers 18:14; Ezekiel 44:29), or if that were not desirable He might put it entirely out of the way, or doom it to destruction (1 Kings 20:42). Such devotement to destruction is often desirable in a world such as ours, so polluted, perverted, abused. There are things which cannot be turned to better account than to be utterly destroyed. There are moral nuisances which can only be swept away by "the besom of destruction." Among these moral nuisances are morally leprous and festering men, who "will not" be healed of their contagious sores. These and their infected rookeries must be swept away. The sooner the better for society at large. God will be glorified in the work of destruction. Hence "anathema," which at first meant something valuable devoted to a god, came, when applied within the sphere of the moral government of the living and true God, to denote objects which had become irreclaimably corrupt, and which consequently He wisely doomed to be destroyed. The apostle disintegrating one particular line of Hebrew thought from amid the complexity of ideas that were woven around the word felt at times that, if the ethical element were eliminated from the case, he could submit to be himself destroyed, even from "the presence of his Lord," if thereby his kinsmen could be constituted heirs of everlasting life and bliss. The destruction of which he thought was thus the annihilation, not of his being, but of substantial elements and factors of well-being.
(J. Morison, D.D.)
Parallel VersesKJV: That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.