Sarai makes a shocking statement:
"The LORD has kept me from bearing children. Go sleep with my maid servant; perhaps I can build a family through her." (NIV) Gen 16:2
First she says that God has prevented her from having children. Is that true? Remember this is a faithful record of what Sarai says and what she says may not be true just because its in the bible. It's a strange thing to say given what God has just promised. He seems to be the one promising children rather than preventing her from having one. It seems to me therefore that Sarai is not talking out of God's promise but her own understandable feelings, desires and disappointments. Perhaps she sees God as the enemy and is angry at him for, as she sees it, preventing her from bearing children. Once we see God as the enemy we tend to take maters into her own hands. Her thinking seems to be "God has prevented me..." but "perhaps I can...". (Her coldness to God is given away again a little later in a laugh when God reiterates his promise.)
Now through, she is not thwarted. Her plan is for her Husband to sleep with her servant which was not at all what God had in mind for them. Imagine how Sarai must have viewed the servant for her to think like that. Imagine the emotional turmoil in store for the servant. Imagine the effect on her marriage to Abram. We are not left to imagine for long as the rest of the chapter gives us the gory details. Hagar despised her mistress (v5), Sarai mistreated Hagar (v6) and Hagar was miserable (v11). Sarai falls out with Abram and he caves into her (v5).
But here is the thing. It makes absolutely no difference to God coming true on his promise and later Abram will get a son through Sara. More on that when we get to it though. For now, I want to think and act not from the dubious deductions of past experience but in line with what God has said in his word. How can I look upon God as my enemy, for when I was his enemy he sent his son to die for me? And I definitely want to avoid wrecking lives by making plans that start from "perhaps I can".