It expresses the standard Christian doctrine that, though God is perfect and people are not, God can still achieve his perfect plan through the imperfect actions of people.

I've never heard it before today. And with good reason. My research indicates that this is an old Portuguese saying. I've read various interpretations. The most common interpretation I saw is that even though our life may not go according to our plan, God will work with it to achieve the result that is best for us. It appears to me that this is a little-known proverb whose meaning is argued about by priests and monks and a few lay people.