8 But you will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth.” (Acts 1:8 NIV)
When we are given a task, expectation has been set that we will complet it to the best of our ability. We may not feel up to the task at hand, but through trying we learn and we accomplish much that we may not necessarily have the skills to accomplish.
In doing so we exercise a part of us and create muscle memory in the doing of a thing. Be that physically or mentally. We learn and we move forward.
If we take this learning and do nothing with it the knowledge will atrophy. These new muscles (mental or physical) must be repeatedly used and flexed. A hard task becomes easy through repetition.
The same is true in our faith life, we must use what we learn or it too atophyies.