We can easily give up on someone when we only see a person's weak points. But God looks at one good point rather than 99 weak points and waits. Some of the disciples of Jesus Christ were lacking in knowledge or were short tempered. But they could be changed to become witnesses of the Gospel because of God's love for them. We should also look for others' merits with eyes of goodness.
"Yet for this reason I found mercy, so that in me as the foremost, Jesus Christ might demonstrate His perfect patience as an example for those who would believe in Him for eternal life" (1 Timothy 1:16).