If you want to benefit from the prayer “Lord Jesus Christ, have mercy on me, the sinner”, you have to give your heart to it. It is very difficult for the mind to be steadfast. But even if an outwardly diffused mind finds concentration, it still isn’t enough.While someone is saying the prayer, he needs to pull the mental power of his mind inwards from outwards. He also needs to give his loving power, too. He needs to give both heart and will.

And if he insists on this work, then devoutness comes into his soul; repentance, humility and the grace of God come; sweetness comes from heaven, brought by the Lord.

By not doing what you like but by being obedient, you can let God break the fort of your established ego.