In the creation account the command to multiply is given together with the command to subdue the earth: “And God blessed them; and God said to them, ‘Be fruitful and multiply, and fill the earth, and subdue it; and rule over the fish of the sea and over the birds of the sky, and over every living thing that moves on the earth (Genesis 1:28).’” He then asked how a farmer (he lived in a largely agrarian society) knows how much land he should cultivate. The answer, of course, is that a farmer seeks to cultivate what he believes he can reasonably handle. He doesn’t take this command to mean that he needs to make his farm be as large as is naturally possible. Likewise, then, it is right for a couple to seek to have the number of children that they believe they can reasonably nurture in light of the other callings they may also have on their lives. In the same vein, Wayne Grudem points out: “We aren’t required to maximize the amount of children we have any more than we are required to subdue the earth all the time—plant, grow, harvest, etc.”
Matt Perman
Website: http://www.desiringgod.org/articles/does-the-bible-permit-birth-control