Little details in the story are touching. The "ten years" that Sarah waited (Gen. 16: 3) before urging Abraham to father a child with Hagar is based upon a custom at the time. Abraham's willingness to follow the custom was because the Lord promised him children, Sarah could not conceive and Sarah urged him to do so. In fact, of the three, Sarah's urging was what seems to persuade Abraham. Her urging is tempered by making it seem she is looking out for her own interests: "it may be that I (Sarah) may obtain children by her." (Gen. 16: 2.) This softens the request, makes it a blessing for Sarah, and casts it in terms which do not belittle or dismiss Sarah. Then, as the account reads: "Abram hearkened to the voice of Sarai." (Gen. 16: 2.)
Abraham was willing to wait on the Lord's promises of children. He was willing to forego the customs that allowed a man to take another wife. It was Sarah's gentle persuasion that convinced Abraham to take Hagar. Sarah was loved by Abraham with his whole heart. It was this great marriage relationship that allowed the Lord to preserve them as the parents of "all righteous." A new Adam for the Lord's covenant people. And, of course, there cannot be an Adam without an Eve. Sarah becomes the "Mother of All Righteous."
This is more critical than most people recognize. It was because of this important relationship that the tenth parable in Ten Parables begins with the marriage relationship. Without this, there was no reason to save the man.
Marriage is separate from its two parties. It has a life of its own. The husband and the wife may be parties to the marriage, but the marriage itself is a separate and living thing. It is distinct from the two partners in the relationship, and greater than either of them. It lives. It is real.
The only people whose right to eternal life has been secured, to my knowledge, came as a result of the marriage relationship and its worthiness to be preserved into eternity. Neither is the man without the woman nor the woman without the man in the Lord. Therefore, if you are interested in eternal life, the very first place to begin is inside your marriage.