James 3:1-18
Just as faith, where it exists, necessarily shows itself in works, so the defilement of the heart sooner or later shows itself in words. Every steam engine has a release-valve through which any excess of internal pressure can escape. If we let this "pressure" build up in us without judging it, it will invariably betray itself in words we will be unable to restrain. Thus the Lord calls our attention to the impurity of our lips (Isaiah 6:5) and shows us from where it springs: the abundance of the heart (Matthew 12:34; Matthew 15:19; Proverbs 10:20). But He invites us to judge ourselves and thus separate "the precious from the vile" so that we might be as His mouth (Jeremiah 15:19).
There is wisdom and wisdom. The wisdom that is from above, like every perfect gift, comes down from the Father of lights (James 1:17). We recognise it by its motives: always pure, without self-will, active for good.
We ought to re-read these verses each time we are about to use our tongues in a bad way: quarrelling, lies (v. 14), running others down (James 4:11), boasting (James 4:16), muttering grudges (James 5:9), swearing or foolish talk (James 5:12; Ephesians 4:29; Ephesians 5:4). Sadly, that means reading them many times each day!