Now the reason why this sign was given, which was only a sign, and which brought nothing to its possessor, and which was a false sign unless the righteousness of faith was in the heart, will be seen when we consider what had taken place after the covenant was made with EVCO 92.3
Abraham. He had entered into an arrangement, the object of which was to work out the promise of the Lord. Abraham and Sarah believed that the promise was to be theirs, but they thought that they must work it out. But since the promise was of an inheritance of righteousness, the thought that they could work it out was in reality the very common idea that men can work out the righteousness of God. So when God repeated the covenant, He gave to Abraham a sign which should always be a reminder of his attempt to work out the promise of God, and his failure. It did not give him anything, but was on the contrary a reminder that he could do nothing of himself, and that everything was to be done in him and for him by the Lord. The cutting off of a portion of flesh showed that the promise was not to be gained by the flesh but by the Spirit. Ishmael was born after the flesh, but Isaac after the Spirit. EVCO 93.1