It simply means that in order for the marriage to work, both the husband and the wife must sacrifice and make an effort to accept, understand, and endure the good, the bad, and the ugly aspects of their partner. "Love is not blind - it sees more, not less. But because it sees more, it is willing to see less." by Julius Gordon

I think it means not just to know each other, but to understand each other. As in comprehending what the other is feeling or where they're coming from... That's what I think at least

The difficulty with marriage is that we fall in love with a personality, but must live with a character. by Peter De Vries ということなんじゃないでしょうか....

Maybe this is an usual tip to keep good relationship between husband and wife.