make an honest woman of someone: o que isso significa?

You've been engaged to this girl for a very long time and now you're thinking of marrying her. When you tell your friend about that idea, he tells you: Finally! It's about time for you to make an honest woman of her. When you make an honest woman of someone, you marry that person. Of course we're talking about a woman. I don't know the origin of that idiom, but its literal meaning gives the idea that a married woman is honest, a lady. So by making an honest woman of your girlfriend for example, you're marrying her.