Is it wrong to use birth control?
As for pills: if it's an abortifacient, then don't use it. If you're persuaded by your doctor or by some literature that a certain pill is really going to unseat a fertilized egg, then I don't think that should be your form of birth control. And if that's your only question in regards to birth control then that should settle the issue for you.
But if you're wondering about the biblical fitness of having any influence in whether you get pregnant, then things get more complicated. My answer is: Yes, there is a place for thoughtful regulation of when children come and how many come.
To explain how I come to this conclusion, let me give you an analogous situation.
Sometimes people ask me if everybody should get married. I say, "No I don't think so." And they say, "What about Genesis 2:18—'It is not good for man to be alone'? You're saying it is good sometimes?" And I say, "Yes, because in 1 Corinthians 7 Paul wishes that everybody would be alone like he is in singleness."
So evidently the fall of man into sin—which happened after Genesis 2:18—and the redemption that comes in Christ affect the natural world order ("It is not good for man to be alone"). They do so in such a way that, under some circumstances, it is better for man to be alone. It certainly was better for Paul to be alone than to be married, he thought, because he was more devoted to Christ and was able to go to jail every other weekend without traumatizing his wife.
Now what about the analogy of that situation to birth control?
Genesis 1 says to fill the earth and be a blessing. Go ahead: have lots of babies, a quiver full of babies. That's natural and normal, and I think we should have lots of babies. I preached on this recently and said to the people in my church with eight kids that we would never scoff at them or make fun of them. We love those big families, and anybody that wants to can have a big family in this church. It is a good thing, if you bring those kids up to be radical soldiers for Jesus.
But if you're celebrating big families then why would you encourage anybody to not have children? Well, just like there is a change in whether or not you marry on account of the fall and redemption, so there is a change in how many children you have and when you have them.
I would simply say: Don't make your choices on worldly principles. This is the killer.
The world thinks children are a pain in the rear and that you should have as few as possible. "The day care center should take care of them, thank you very much, because I have other things to do. Don't get in my way." Children are just a bother. But that is a totally non-Christian way to think.
We should make our decisions on Kingdom purposes. If—for Kingdom reasons, gospel reasons, advancement reasons, and radical service reasons—having another child would be unwise then I think we have the right and the freedom to regulate that. But such regulation must presuppose that we're not doing anything like abortion to measure out when and how many children we have.