Proverbs 26:23

Like the glaze covering an earthen vessel
    are fervent lips with an evil heart.

Glaze can cover and hide what is underneath while giving the appearance of revealing its inner substance. We can see the clay, but the glaze covers over any imperfections and causes the clay to have an alluring shine that it really doesn’t possess itself. In the same way we may use our lips and words to cover over and give the wrong impression of our hearts.

Fervency does not equal sincerity. Some speak fervently with the intention of covering up their evil intent. Others speak fervently to win people over by the power of their personality. It is not speech that measures the sincerity of the heart, nor does speech ultimately reveal the heart. What reveals the heart is the long-term obedience of BOTH words and actions, and that provides the most reliable test. That obedience is not something performed as a duty but one that bears the fruit of the Spirit—love, joy, peace, patience, kindness, goodness, and self-control. This fruit is something that is unmistakable and flows naturally from a regenerate heart.

Fervency and personality are not necessarily wrong things, but don’t use them to measure sincerity or depth of character. Look at the fruit of a person’s life—the fruit they bear and the fruit of their lives, i.e. the impact on others around them. By doing that, we will not be taken or fooled by a “personality,” no matter how fervent it may be.