“…for God sees not as man sees, for man looks at the outward appearance, but the LORD looks at the heart.” (1 Sam 16:7 NASB)
The logic why beauty shouldn’t matter to Christian men goes like this: God doesn’t look at the outward appearance. Christian men should be like God. Christian men shouldn’t look at the outward appearance. Christian women then follow up on the conclusion and don’t do even minimal efforts to make themselves look good. They let themselves get fat, don’t fix their hair, cut their hair short, wear pants instead of shorts or dresses, don’t wear makeup, etc.
The problem with this logic is that men will never see as God sees. Scripture explicitly states that man looks at the outward appearance and cannot see the heart. Men can see beauty and behavior, but those aren’t the heart.
However, much Christian teaching asserts that men should feel ashamed for being so superficial as to be attracted to feminine beauty, which it calls “outward beauty”. Teaching frequently asserts that men should be attracted to inner beauty and implies that men should feel ashamed for not being attracted to inner beauty–things like femininity, sweetness, and warmth. These are all good characteristics and men should look for them in a woman, but they will never generate sexual attraction, which is reserved for feminine beauty alone. Bad behavior may obviate sexual attraction, but that doesn’t mean that good behavior can generate it. Man is hardwired to be attracted to feminine beauty.
Man is hard-wired to find feminine beauty attractive; we see this all throughout the Song of Solomon where a woman’s beauty is extolled in exquisite detail. The teaching in the Song of Solomon is clear that sexual beauty is part of the natural order of things and is nothing to be ashamed of; there is nothing to be ashamed of in feeling attracted to sexually beautiful women. God created men so that we would be attracted to feminine beauty; the Song of Solomon affirms that attraction.
Christian women, take note. If you want a husband, you must be sexually attractive. This means doing things to make yourself physically attractive: staying slim, fixing your hair, wearing feminine clothing, wearing makeup, doing your nightly beauty ritual, wearing your hair as long as you can, etc. This doesn’t mean that you shouldn’t behave in an attractive manner. Of course, you should be feminine, sweet, warm, fun, etc. Those are not a substitute for doing what you can to make yourself physically attractive.