Genesis 16

"Sarai said to Abram, 'Since the Lord has prevented me from bearing children, go to my slave; perhaps I can have children by her.'"

Genesis 16:2

I've heard it said before that this is a show of Sarai's faith - that she's willing to let her husband sleep with her servant so that God's promise can be fulfilled.  I think that's a load of horse manure.  If that were the case, she wouldn't have gotten so peeved with Abram, and she wouldn't have treated Hagar so poorly.

I can't believe that Abram was 86 years old at this point and still hadn't learned the most important lesson of marriage: when your spouse tells you it's okay to do something that you know upsets her, she's really telling you that you'd better not do it!  Sometimes, it's hard to tell the difference between this and an honest approval, but if your wife is telling you to sleep with another woman then you know it's a bad idea.

On the other hand, there's also a lesson to be learned here from the woman's side: don't tell your spouse to do something that you don't want him to do!  He'll be egg-headed and do it, and then everyone involved will all be mad at each other.

Of course, the same situation often happens in the reverse direction as well, where the man tells his wife to do something and then gets mad at her for doing it.  The story goes both ways.  Men and women alike need to learn both of these lessons, and not just apply them to marriage but to all types of relationships.  To keep it simple: (1) always tell the truth, and (2) don't do something that you know is wrong just because someone told you to do it.