The second way Paul illustrates the humility of this sound judgment is by saying that faith is a gift. If you come to terms with the fact that God measures out faith in various measures you will think with sound judgment and you will not think more highly than you ought to think. That is thinking more highly than one must think. Because, even though faith is indeed an act of the human heart, it is first a gift from God. God gives grace and God gives the faith to receive the grace.
All boasting is excluded.
To grasp this is to be freed from thinking more highly than we should and to think with sound judgment. The clear meaning is that God measures different measures of faith to different people. This is mentioned in verse 6 as well when the list of gifts begins with prophecy. So the first way Paul shows us what sound judgment is is by telling us that he and we fulfil our role in the church only by the grace that is given to us. Secondly he says that the differing measures of faith that we have are owing to God's measuring out different measures of faith.