It is a psychological fact that when we are determined to achieve a goal, we develop a faith in the goal and a confidence in ourselves. This faith is what ultimately takes us to success. The Lord explains that He rewards the supplicant only by making faith in His devotee more firm.
Faith is a growing belief that is rooted in understanding. As faith increases, the mind becomes more and more efficient. A single-pointed mind is a mighty force against which no obstacles can stand for long. Success is directly proportional to the depth of faith we have, both in ourselves and in the goal.
Lord Krishna adds that, faithful activity always brings about success, but the very existence of the field of activity, the ability to act, the fervour of faith that supplies consistency to all efforts – all these are possible only in the medium of the Supreme Consciousness, the Self.