Through faith we rely not on what we have done for God but on what he has done for us. That is the basic thing the disciples needed to know about the nature of faith, before they could have any at all, let alone seeking to increase their faith. It was to be accepted as a free gift, quite undeserved. It is a difficult thing for people to accept today as it was in the time of Jesus. We often hear talk of the value of self esteem.
Teachers try to increase the self esteem of the children in their care.
It is often stated as one of aims of a school. Managers in business find it is helpful to encourage workers and so to increase their self esteem for the sake of the company. If you are applying for a job you are expected to value your own worth highly. Confidence is all the go. If you don't have it there is something wrong with you, it seems.