Let your life match your lip.
There are far too many Christians who live two different lives: one on the inside, another on the outside; one Sunday morning, another the rest of the week.
Such people are hypocrites, phonies, Christian liars; they live wrong lives. Why? Because they have a wrong heart. We must be very careful that our heart is clean and pure (see Psalm 51:10).
We are told in Matthew 12:34 why our heart is so important: For out of the overflow of the heart the mouth speaks. In other words, your heart affects your mouth.
Since our lives, and especially our words, are being examined by unbelievers, we must be careful to have a clean heart so that we will have clean words; and if we have clean words, then our lives will show good fruit. In other words, a good (spiritual) heart will bear good fruit.
No good tree bears bad fruit, nor does a bad tree bear good fruit. Each tree is recognized by its own fruit. People do not pick figs from thorn bushes, or grapes from briers. The good man brings good things out of the good stored up in his heart, and the evil man brings evil things out of the evil stored up in his heart. For out of the overflow of his heart his mouth speaks (Luke 6:43-45).
Therefore, be careful that your words are clean and pure and that your actions are equally clean and pure so that the world will see that your life matches your lip.