Genesis 16:2 Sarah took it into her own hands to help God’s plan along believing that Abraham’s heir would come through her maid servant. This was practiced in the ancient world.
Genesis 16:3 Hagar became Abraham’s second wife, though not on equal par with Sarah. Why Abraham according to the text readily agreed, it is not known. It is possible that after 10 years he figured that Sarah could be right. What he should have done waited for the Lord’s answer.
Genesis 16:4 Hagar looked down at Sarah, possibly because she felt now more superior that she was able to produce an heir for Abraham. As a servant of Sarah, it was wrong for Hagar to have these thoughts.
Genesis 16:5 Sarah puts the blame on Abraham. Why she does this is not clear. It wasn’t Abraham’s fault she barren.
Genesis 16:6 Abraham, not wanting to offend his wife in anything he might say, simply turned over the responsibility to Sarah to deal with. It is possible that Abraham’s first thought when accused by Sarah was, “It was YOUR idea.” The human solution to Sarah's barrenness creates new problems.
Genesis 16:7-9 God sent His Angel upon hearing the cry of Hagar to make sure she was cared and provided for by Abraham and Sarah. Again, this wasn’t Hagar’s fault that she was made wife and bearer of Abraham’s child. I would almost bet that Sarah, knowing that Hagar fled, was happy and didn’t want her to return. God sees things differently and obviously doesn’t approve of Sarah’s behavior. God also didn’t approve of Hagar’s behavior and tells Hagar to return and to submit to Sarah’s authority.
Genesis 16:10-12 God promises Hagar that a son will be born, actually gives the name of the child Himself, Ishmael (Which means God hears) and he will be great and also have a great number of offspring.
Genesis 16:10-12 He shall be a wild donkey of a man. The untamable desert onager (wild donkey) best described the fiercely aggressive and independent nature Ishmael would exhibit.
Genesis 16:15 By naming Ishmael, Abram publicly acknowledges him as his son and heir. Abraham is now 86 years old, the 11th year after settling in Canaan.