If you were to ask most people inside and outside the church, what a "Christian" was like, you might get answers like:judgmental, narrow-minded, hypocritical, naive--you know them all. On the other hand, you might get: nice, generous, gentle, kind, helpful. We would really hope for: loving, joyful, peaceful, patient, good, faithful, forgiving (Galatians 5:22 et al). We can look at a list like this and know we cannot do this very well. First thought: suck it up, bring on the will power, and try, try, try. Now add the practical applications of all these, and it really gets overwhelming.
It's easy to understand the principle if we look at the negative side. We all know how hard it is to maintain the will power to avoid overeating, addictive behaviors, anger, gossip, selfishness, etc--we know what these are as well. Knowing right from wrong is important, but only the first step. The Israelites had the commandments for 1500 years, and never got it right. Doing right and not wrong on our own is hard. Doing it joyfully and gracefully on our own is impossible.
We usually think of freedom as being able to do what we want. The question then becomes what we want. It has been said that true freedom consists not in doing what we like, but in having the will to do what we ought. We usually don't have the power to want what we know is right--that is what philosophers call "Moral Freedom" and it requires not our own will power but sacrificing our own selfish will.
I used to wonder about Jesus' statement in Matthew 11:28-30 that His burden is light--it looks hard. The reason that our burden is light that He stays in the harness with us, and carries the load. All we have to do is stay in harness and go in the same direction. In other words, follow His leading, stay on His path.
But just going with Him is not enough Judas was a fellow traveler, not a Jesus follower. He apparently liked being part of Jesus' entourage, but kept missing the point of who Jesus was and what he was doing. When the going got tough, he got out. Are we willing to give up our own will and take His will and follow it?