Sin is what you do when your heart is not satisfied with God. No one sins out of duty. We sin because it holds out some promise of happiness. That promise enslaves us until we believe that God is more to be desired than life itself (Psalm 63:3). Which means that the power of sin's promise is broken by the power of God's.
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 PiperWhat was once foolishness to us-a crucified God-must become our wisdom and our power and our only boast in this world.
John PiperIf you alter or obscure the Biblical portrait of God in order to attract converts, you don't get converts to God, you get converts to an illusion. This is not evangelism, but deception.
John PiperA saving knowledge of Christ crucified and risen is not the mere result of right reasoning about historical facts. It is the result of spiritual illumination to see those facts for what they really are: a revelation of the truth and glory of God in the face of Christ-who is the same yesterday today and forever.
John Piper