Many things—such as loving, going to sleep, or behaving unaffectedly—are done worst when we try hardest to do them.
So true, but Lewis didn’t mention the self-control required to do those things without trying.
Did I hear you say, “That’s nuts!”? Well, it’s not nuts. The only way to develop positive behaviors so you do them automatically is by developing the appropriate habits, and that takes self-control.
What motivates those positive habit formations? God’s Holy Spirit, working through frequent exposure to, study of, and meditation on his Word. That is the very first godly habit, and all the others flow from it. When God opens your eyes to the awful wonder of Jesus’ sacrifice on the cross for your sins, and the depth of his love for you—personally—that motivated him to submit to that torture, you will want to let him speak to you through his Word. God will show you that he is love, and as Jesus demonstrated his love by dying on the cross for you, so you will want to demonstrate your love for him by crucifying your own desires for self-gratification, and obeying him even when you don’t feel like it.