Call Him Ishmael

In the last couple of verses, Sarai decided they were going to try and have a baby through her maidservant since there hadn't been any babies yet. We talked about why that was such a boneheaded move, and now we'll look at some of the consequences of trying to achieve in the flesh what God promised in the Spirit.

[Genesis 16:4-6]
After they go through with it, and Sarai's maid becomes pregnant by Abraham, the maid gained some animosity towards Sarai (To no one's surprise.) Sarai admits her mistake, but acts like a jerk towards Hagar until she ends up running away from camp.
Works of the flesh breed pride, competition, and contempt. You see this frequently when "accountability partners" go awry. In an attempt to force by the flesh what God promised as a work of the spirit, well-meaning discipleship groups start up things snapping yourself with a rubber band when you have negative thoughts or kicking each other in the nuts every time you look at porn. Everyone who has tried this knows that, at best, this results in red wrists and sterility, and at worst results in shame, dishonesty, and ruined relationships. Hagar was mad at Sarai for convincing her to go along with this stupid plan, and Sarai was mad at this woman who was carrying her husband's baby. Fleshly attempts at fake righteousness destroy relationships.

[16:7-11]
It's interesting that, despite their stupidity, Hagar's child was still a child of Abraham, and God had promised Abraham that He would bless his children. God's not one to skip out on a deal, so an angel informs Hagar that she can safely return to camp and that her children will be numerous just like Abraham was promised.
It's good to know that, even when we do something stupid, God is still God and His promises do not change. We can screw up and complicate things, but we can never stop the promises of God. So if God has promised you something and you ran away from it, it's still a promise and you can't destroy it completely.

[16:12-16]
This promise fulfillment came with a bit of catch though: this son is going to be a bit crazy and pretty much everyone is going to hate his guts. This had immediate fulfilment when Abram eventually had a song through Sarai, and that son and Ishmael didn't get along very well, and it had future fulfillment in that Ishamel's descendants founded Islam where Issac's descendants founded Judaism. God fulfilled the promise of fruitfulness to both descendants, but they were destined to be at war for the rest of their existence.

Similarly, there are people who will always hold to a fleshly, self-made righteousness. And while they may still be successful to a degree, they will always be at war with those who hold to the true promise of salvation by Grace through the finished work of Jesus. There will always be works-obsessed Hagars giving birth to book-burning, event-picketing, skirt-measuring Ishmaels, and they will "dwell in the presence of all [their] brethren." We can help each other out, and we have no excuse to be mean to each other, but this grace vs. works split will always be present in the church.
It's a tough thing to deal with, because it leads easily into "You disagree with me! You're an Ishamel! Burn the witch!" if you're not careful. It's easy to lash out at anyone telling you to stop being an idiot and say "I do what I want, you Pharisee!" when you are legitimately being an idiot. But there will always be Issacs and Ishmaels, and there will always be lazy people using it as an excuse to not have to put any effort into their lives. I think this is why the Bible warns us to not freak out over other people's convictions and to leave the ultimate judgement to God without kicking out everyone who disagrees with us.