God's purpose for marriage is a recurring idea. Understanding earthly life as an education designed to establish a foundational understanding of the character of God allows Lewis to view marriage as another of the courses in that education and to examine it for the wisdom it offers. Lewis acknowledges the marked differences in the tendencies of the sexes toward the characteristics that distinguish them; but rather than allow them to remain as "a sword between the sexes", Lewis follows the biblical idea of man and woman created in the image of God (found in Genesis 1:27) through to its logical and useful conclusion. If each of the sexes carries a part of the whole image of God, then their union and harmonization would provide a more complete image of God.