God is able to do great things for those who trust him; but he is not interested in those who boast in their accomplishments after the fact. For instance, when Gideon gathered 32,000 soldiers to fight against the Midianites, God sent home 31,700 of them because they would have boasted once the battle was won. He chose a mere 300 to attack an army described as "locusts in abundance." This tiny army won the battle using a unique night attack. But it all worked because the Lord was with them. Read the whole account in Judges 6-7.
This same thought is carried over into the New Testament. In 1 Corinthians 1, Paul told the Corinthian church that they were foolish to take pride in the Christian teacher each was following because the power of the gospel is not in the messenger but in the message of the cross! And if you are ever tempted to take pride in "your" spiritual accomplishments, read the conclusion of the chapter. God has chosen the weak, foolish, and low so that we have nothing to boast in but him. And that's the way it ought to be.