If you don't feel strong desires for the manifestation of the glory of God, it is not because you have drunk deeply and are satisfied. It is because you have nibbled so long at the table of the world. Your soul is stuffed with small things, and there is no room for the great.
John PiperThe assurance of the believer is not that God will save him even if he stops believing, but that God will keep him believing--God will sustain you in faith, he will make your hope firm and stable to the end. He will cause you to persevere.
John Piper