I received a question on my last blog post, and I started writing a very voluminous answer such that I decided to just post it as a new post, for more visibility. The question is with respect to the "conflicting instructions" that were given to Abraham, and essentially how should Abraham have responded to the situation he was placed in.
"but God also asked Abraham to have a child that he could only have by having intercourse out of wedlock, then should we conclude that God was expecting Abraham to use his judgment as to reconcile the conflicting instructions in a manner most consistent with honoring God?"
Calling it conflicting instructions is a bit of a stretch. God never "instructed" anybody regarding Sarah's barrenness, it was simply a noted fact. Here's the order of events with Abraham/Sarah/Hagar:
God says, you will have a son (to Abraham), specifically saying "of your own body" meaning his physical descendant, but not necessarily Sarah's;
"Now Sarai, Abram's wife, had borne him no children";
Sarah then offers for Abraham to sleep with Hagar, to "build a family through [my maidservant]", which Abraham does having a son;
13 years later, God comes again and says that Abraham will have a son through Sarah, and that he would be the 'child of the promise', that is, the son that God had promised to Abraham at the beginning.
So like I said, there was no instruction for Sarah to not have a child, it's really more like reconciliation of the promise (you will have a son) with its apparent non-fulfillment (Sarah was barren). In that situation, at Sarah's suggestion Abraham slept with Hagar to produce the son they were expecting, and 13 years later God comes in and clarifies that the son he had (Ishmael) was not the son promised before (although God doesn't say this directly, many commentators implicitly read it from what God does say about Isaac)
This is where I think a lot of commentators come into disagreement, over this question: did Abraham sin by sleeping was Hagar? I think there are a lot of valid perspectives on this question, one of which I raised (the issue of marriage being between one man and one woman), but there are many other perspectives about how Abraham should have responded to the promise, should he have just waited for Sarah to have a child when they thought it was impossible? Etc.
Nevertheless, it seems inaccurate to say that God gave conflicting instructions, but there is definitely a conflict between promise and reality. This is a very common theme in the bible, and it's very much related to the issue of faith, or as Paul puts it, the "things visible" and "things invisible" (2 Cor 4:18). How does one reconcile the unseen promise ("I am with you", Matt 28:20) with the present reality (I don't see Jesus right now)? It's a very deep subject that I'm not really going to address, other than to say that this is very related to Abraham's situation.