By Abraham listening to his wife, who had not believed God as he had, he was brought down to her level, the old level of natural cause and effect. (Gen. 16.) According to nature Abraham's belief was folly. So it appeared to Sarah.
Accordingly she took the common sense view of the matter, and said the thing must be brought about by natural means. Not so are the purposes of God wrought out, and not so does the just man live the life appointed for him.
The result of natural cause is natural effect; the bondwoman produced a son who by nature was not, and could never be, the son of promise. He lived and became the father of a race ever at enmity with the seed of promise. This is God's way of pointing out that the just must live by faith.
It is no use attempting to bring God's purposes to pass by our own wills, in our own time, by natural means. The only result will be a crop of thorns that will give us many a sore thrust and many bitter reflections. Still God will use even our crop of thorns to His own ends and our blessing. His government is grace.
S. H. H.