Imam al-Haddad (may Allah have mercy upon him and benefit us by him) explains that your speech is a reflection of your inner state.
“Your words are the fruit which you produce. So observe them: are they foul or are they good? What you find is what you are, for they are a part of you. A pure container only pours out that which is pure; and the opposite is true. Likewise, a good palm tree, or any tree, produces good fruit; and a foul tree produces foul fruit. ‘Every container gives of what it is contained within it.’ Allah the Exalted says: The good land produces abundant vegetation by the will of its Lord, whereas the foul land hardly produces anything (7:58).”
Source: Tathbit al-Fu’ad, Vol 1, p.27