The Law of Life is more powerful and active than anything generated or maintained by self-effort. With self-effort I am always at the mercy of how I feel. If I feel spiritual then I can pray for hours at a time. But if I do not feel spiritual then I cannot even pray for five minutes.
This is why so many believers live their lives like a roller-coaster. They do not live according to principle, according to the Law of Life. Thinking it is up to them to become Christ-like, they turn an easy yoke and a light burden into a difficult yoke and a heavy burden – difficult and heavy for themselves, and for those who must live and work around them. The one who rests in Christ will produce more fruit than the one who strives with self-effort.