Ten years had passed since God had first promised Abraham descendants, and now three years had gone by since God had reassured Abraham of this same thing.
Whereas in Genesis 15 Abraham is seen as a man of faith, in chapter 16 we see him as a man of unbelief. He could wait no longer for God to fulfill His promise.
A lack of patience tends to foster unbelief. In chapter 15 Abraham believed the Lord; in chapter 16 he hearkened unto the voice of his wife. In chapter 15 Abraham walked after the Spirit; in chapter 16 he walked after the energy of the flesh.
What a sad inconsistency in the life of this man of God. Only Jesus Christ could say, "I do always those things that please him" (John 8:29).
Abraham was tested by the suggestion of a well-meaning wife. Would he take matters out of the hand of God and act in the energy of the flesh?
This test was the trying of the patience of his faith. Would he wait on God to fulfill His word in His own time and way, or would Abraham's patience give out and the flesh take over? God wanted him to have a mature faith.
What would you have done in his situation?