It refers to the past process of being completely persuaded with the result that one has confidence, conviction, trust. For our rejoicing is this, the testimony of our conscience, that in simplicity and godly sincerity, not with fleshly wisdom, but by the grace of God, we have had our conversation in the world, and more abundantly toward you. Union with Christ depends upon a person's faith in Jesus Christ and His substitutionary atonement on the Cross. He had a powerful source of strength. He explains how he is strengthened, and he passes this confidence along to his readers.
Confidence breeds confidence.
A leader can draw attention to the big picture and, especially when times are tough, give his subordinates confidence in the outcome. There is always every reason to be encouraged in the Christian life. We share in Christ's victory over Satan and his forces. There is no charge for Grace Notes Materials. The ministry is supported by Christians who pray for the work and share in the expenses.