Paul knows that when we are weak we depend on God to be our strength. In our weakness God's grace is more than sufficient to carry us in the most trying of circumstances.
When we know that God has spoken to us, it removes any fear we might have had.
In my own experience, one word from God erases years of self doubt, negative esteem, and words of discouragement spoken to us by others.
God speaks words of encouragement to us when others tell us things won't work out or we are foolish in taking a step of faith.
I have found with women that many times we run to others for answers instead of going to the Lord. In doing so we often lose out on hearing from God, since we have already decided to take the advice of others.