I don't think the text bears out this interpretation. I think it was more of an "Oh, c'mon...Really?" type of response. I think Abraham got impatient and resigned himself to God's promise being fulfilled through Ishmael.
He believed Him in Gen 15, and in Gen. 12, but that doesn't mean there was never any doubt, ever. The text seems to point to doubt here in Gen. 17, and who could blame him? First, Abraham complains that his "steward" will have to be his heir, then God says "This shall not be thine heir; but he that shall come forth out of thine own bowels shall be thine heir." (Gen. 15:4 KJV) Note that nowhere in the text of Gen. 15 does it mention that Sarai would be the mother. OK, so if Sarai can't bear children, wouldn't it make sense that someone else would have to be the mother? Sure, enter Hagar. Abram and Sarai honestly think this is God's will, I believe, so Abram has Ishmael with Hagar and all is going according to plan, in Abram's mind. Then, 13 years later God comes along and says that Sarai will bear a child at 90 years old. First, Abraham thinks that Ishmael will be his only heir, then all of a sudden, out of a clear blue sky, God appears and says "change of plans, your 90 year old sterile wife will bear you a son". It's more of surprised shock and disbelief than joy, I would think.
No doubt (pun intended)
God surprises Abraham with the news that his 90 year old sterile wife will bear him an heir. Sheesh, I would laugh and doubt too. Certainly, he loved his son, Ishmael. His reaction concerning Ishmael can only be interpreted as doubt, though. If he "believed" that God would bring forth a son through Sarah, why did he say "
O that Ishmael might live before thee!" (Gen. 17:18a KJV)? Other translations say:
“
If only Ishmael might live under your blessing!” (NIV)
"
O that Ish'mael might live in thy sight!" (RSV)
What would your first reaction be if confronted with this situation? I might ask "what about Ishmael?" Or "I thought Ishmael was going to be my heir". Abraham is
not accepting God's premise. God is saying "there's going to be another heir through Sarah" and Abraham is saying "Oh, come on, Sarah is 90 years old and sterile. Just let Ishmael 'live in thy sight' or 'under your blessing'". If he wasn't doubting, he would not have tried to keep Ishmael as the heir of the covenant, no matter how much he loved him.
OK. But I don't see much of a difference between her laughter and Abraham's.
"
Therefore Sarah laughed within herself, saying, After I am waxed old shall I have pleasure, my lord being old also?" (Gen. 18:12 KJV)
She doubted too, but it was because she and Abraham were abstaining from relations due to age. I really don't see how Sarah's laughing at the premise and Abraham laughing at the premise are any different. They both seem to be doubting God, but for different reasons.
Welcome to the fray.
As has been said, more than once here, then can we disobey God and still be saved?
Yes, obedient faith and belief.
I don't think God will "leave or forsake you" for any reason, but we can push Him away by our disobedience.