Now we, brethren, as Isaac was, are children of promise. But, as he who was born according to the flesh then persecuted him who was born according to the Spirit, even so it is now. (Gal 4,28-29)

This never-ending struggle between flesh and Spirit will continue throughout human history. Ishmael characterizes the fruit of what man can do, what he can handle in his strength - this fruit, of course, takes the outward form of godliness, just as Abraham sought to present Ishmael to God in order to obtain for him the seal of heaven. This is generally the way of all religions, including much of what is presented as Christianity today.

Isaac, on the other hand, is synonymous with that which is impossible for man, that which he cannot do, that which must be done sovereignly by God. From salvation, for which we can do nothing, to victorious life in God, which is not achieved by the power of asceticism or willpower. Both are God's gift, they come by the miracle of the birth of new life. This refers both to "eternal life" as the salvation of the individual, as well as to "life in the Spirit" as our daily walk in the victory over sin.

This fierce struggle of flesh against Spirit has been going on throughout history, "as then that which was born of the flesh persecuted that which was born of the Spirit..." Spiritual things on this earth suffer oppression, persecution, non-acceptance. Little Isaac did not understand at all what made him unacceptable to Ishmael, why he became the center of his hatred, for he had not yet done anything to him. The simple fact that he was born, unexpectedly and miraculously, was enough; it made him a precious gift from above to Abraham, and it stirred up strife. The heavenly birth provokes the hatred of the flesh, of the powers from below. As soon as there is light from God anywhere on earth, darkness launches a battle against it to devour it. For even the birth of Christ was paid for not only by the lives of the babes of Bethlehem, but later in the history of the Church by the multitudes who suffered for the glory of God in later centuries because they came to know the truth. Their persecutors were overwhelmingly religious people.

But the good news is that, despite all the oppression, the darkness did not swallow up the light (Jn. 1:5) and it will never do so.