Isaac, unlike Ishmael, was not the product of Abraham's strength, for Abraham had become sterile by then. Isaac was born through God strengthening impotent Abraham. This is the type of service that lasts for eternity. One " Isaac " is worth a thousand " Ishmaels." All " Ishmaels " will have to be cast out finally. Abraham could keep Ishmael for some time, but finally God asked him to cast him out (Gen. 21:10-14). Only Isaac could remain with him. There is a spiritual lesson here. That service which is the result of God working through us, will alone remain for eternity. Everything else will be burnt up. You may have heard the saying, " Only one life, it will soon be past; only what's done for Christ will last." It would be more accurate to say, " Only what Christ does through me will last." Paul lived and laboured according to God's living and working through him (Gal. 2:20: and Col. 1:29). Hence his life and labours were so effective. He lived by faith and he worked by faith.

In Genesis 16:16, we read that Abraham was 86 years old when Hagar bore Ishmael. In the very next verse (Gen. 17:1), we read that Abraham was 99 years old when God appeared to him again. We see here a gap of thirteen years. Those were years when God waited for Abraham to become impotent. God could not fulfill His promise, till Abraham had become impotent. This is God's way with all His servants. He cannot work through them till they recognise their impotence. And in some cases, He has to wait for many years.

Abraham needed to learn what it really meant to trust God. He had to learn that it was only when he became impotent that he could truly exercise faith. In Romans 4:19-21, we read that although Abraham knew that his body was impotent to produce a son, yet that did not worry him. He was strong in faith and glorified God by believing that God was well able to perform what He had promised. He did not waver in unbelief, for his feet stood firm on the rock of God's Word to him. But when could Abraham exercise such faith? Only when he had come to an end of all confidence in his own ability. We too can exercise real faith only when we reach that state of utter helplessness. This is God's way, so that no flesh may ever glory in His presence.

This does not however mean that we do nothing. No. God does not want us to be reduced to a state of inactivity. That is the other extreme of error. God used Abraham to produce Isaac. God didn't do it all by Himself, for Isaac was not born, apart from Abraham, through a virgin-birth. No. But there was a difference between the birth of Ishmael and the birth of Isaac. In both cases, Abraham was the father. But in the first case, it was in dependence upon his own strength; in the second, in dependence upon the power of God. That was the difference - and what a vital difference!