Agreement between one’s life and one’s witness is the first requirement for proclaiming the Gospel. Not practicing what you profess is therefore hypocrisy, a betrayal of the Christian duty to be “salt of the earth” and “light of the world”.
Paul was the one who reminded the Church in Corinth: “You show that you are a letter from Christ … written not with ink but with the Spirit of the living God, not on tablets of stone but on tablets of human hearts” (2 Cor 3:3). Christians themselves, not the things they say, are Christ’s “letters of recommendation” (2 Cor 3:2) to the world. (YOUCAT question 345-347)
Hypocrisy implies a double standard in the morality that one practices publicly or implicitly. Externally a hypocritical person advocates goals and values that he does not respect privately. “Little children let us not love in word or speech but in deed and truth.” (1John 3:18)