In this one verse appears several important, foundational points that relate to marriage. The first is that God created both men and women in His own image.
Before God, a man and a woman are equal, meaning that both have the same potential: to be transformed into the image of God and inherit His Kingdom. Marriage, then, is a union of equals before God. However, Scripture clearly shows that God placed husbands in the position of authority—he is, as has been said, first among equals.
Yet, though they are equal in potential, they may or may not be equal in many areas of mental and physical abilities, and they are certainly not the same in emotional makeup or strength. It is evident that men and women have different natural inclinations, skills, and abilities—all the while not making one better than the other.
Being fashioned after God's own body and mind implies that both have human equivalents of God's abilities, desires, goals, preferences, etc. While creating Adam and Eve, God took many of His qualities and distributed them between male and female humans. Clearly, humanity's God-like qualities are not as excellent as His, since there is a great gulf between what God is and what humanity is, but we have human-level counterparts of what God Himself possesses. We are made after the God-kind.
That fact makes the relationships that we undertake with others quite important. Genesis 1:27 make it apparent that we are no longer dealing with just physical associations. In His first mention of mankind in the Bible, God begins by putting man's existence on a spiritual plane by letting us know He made us in His image. Our relationships, then, also have a God-plane quality to them, suggesting that we need to take them very seriously.
Why? Because the goal of every human being, whether he or she realizes it or not, is to be just like God. Male and female, created in God's image, are on the same track to the same place. So, the relationship between a man and his wife assumes a very spiritual and imperative quality.