I have often heard it taught/assumed that Abraham having Ishmael by Hagar was an act of unfaithfulness on his part, but I’m not so sure that’s the case.
The assumption is that Abram and Sarai didn’t trust in God’s ability to give them a son naturally, so they sought out a way to make it work on their own because they doubted God.
What first made me question this is that when God speaks to Abraham about having a son in chapter 17, Abraham brings up Ishmael and doesn’t seem at all ashamed about it. If Abraham knew he was doing something wrong in siring Ishmael, when God comes promising another son, would he want to draw attention to his rebellion? Maybe he would realize that God was more serious than he originally thought in promising a son, but I can’t imagine he would interrupt to say, “Let that son you’re promising be Ishmael,” if he truly believed he was being faithless in having him.
The Hagar thing still seemed odd to me though until I realized that it’s the same thing that Jacob’s wives do unabashedly. When Rachel isn’t able to bear any children, but wants to compete against her sister Leah who is bearing Jacob son after son, she gives him her servant to bear children on her behalf. Leah then does the same when she stops bearing children. I realized that I am approaching/considering this question from a modern western perspective that assumes monogamy, making the bearing of a child with your wife’s servant an act of adultery, but that was far from their assumption. It was completely normal (and maybe expected), especially for a patriarch of a large family, to have multiple wives and/or concubines. The fact that Jacob, in a couple generations from Abraham, had two wives and two concubines, and clearly didn’t see that as problematic, tells me that Sarai giving Hagar to Abram to bear a child on her behalf would likely have been culturally normative.
If this is culturally normative, then it completely changes the way we would need to consider this interaction.
The analogy that comes to my mind now is if my family was living in an apartment, wanting to move to a house, but struggling to afford what we needed in a house, and God showed up and promised that He would give us a house. Because God promised, my wife and I start looking with renewed determination and eventually find a house that would suit our needs and, seemingly miraculously, is in our price range with nobody outbidding us. So we buy the house and praise God for keeping his promise to give us a house. A decade later, then, as we are living in the house we believe God provided for us, God shows back up and says, “I’m going to give you a house.” What would our reaction be? Probably something like, “Wait, another one? You’ve already given us one house, and now you’re going to do it again?” Maybe then in another year someone would show up at our door and hand us the deed to the house that God was giving to us, but does that make our looking for and purchasing the house we did an act of disobedience or faithlessness? Not at all! We only continued looking and ultimately purchasing the house we did because we thought we understood what God was promising and we were trying to be faithful to that. Buying that house, while not what God was ultimately promising, was done in an attempt to be faithful to Him, not in an act of unbelief.
So if Abram and Sarai are living in a culture and time where it is normal (or even expected) for a man as rich and powerful as Abram to have more than one wife/concubine, and/or where bearing a child by your wife’s servant is considered as bearing a child to your wife, then might Ishmael not have been very similar to buying that house? Trusting that God promised He would give them a child, they began looking for how that could happen, and decided to take the totally normal and acceptable means to bear a son for Sarai through Hagar. So then when God showed up to renew His promise, clarifying that He means that Sarai will bear him a son, it makes sense for Abram to be confused by it because, hasn’t he already had a son by Sarai through Hagar?
This is why I question the assumption that Abraham having a son by Hagar was necessarily an act of faithlessness. In fact, it seems to me, though I admit I could be wrong about it, that Abram and Sarai decided on this course of action specifically seeking to be faithful to what the Lord had said.