‘But the tongue can no man tame. It is a restless evil, it is full of deadly poison. With it we bless the Lord and Father, and with it we curse men, who are made after the likeness of God.'
For the one thing that is untameable is the tongue. It is a restless evil, ever at work doing harm and causing problems, and in the end making men spiritually ill and permeating their whole being with poison (compare Psalms 140:3 - ‘they make their tongue sharp as a serpent's and under their lips is the poison of vipers'. See also Romans 3:13, "With their tongues they have used deceit; the poison of asps is under their lips"). It may sometimes appear to be tamed, but its wildness will soon manifest itself if it is taken off the bridle.
And how inconsistent the tongue is. At one time it blesses ‘the Lord and Father', the Lord of creation (Malachi 2:10; compare Malachi 1:6; Isaiah 64:8), and then at another time, sometimes very soon afterwards, it curses the very lords of creation whom God has set in place, who have been made in the very likeness of the God they bless (Genesis 1:27-28). They can even curse those who are the very representatives of God. James is using a powerful word in ‘curse' but it covers anything which is said to the detriment of others, right up to the worst of all, the actual curse. Compare John 7:49. Here are doubleminded men indeed (see James 1:8).
This idea of ‘blessing' was especially relevant to a Jew, and therefore to many Jewish Christians. Whenever the name of God was mentioned, a Jew had to respond: "Blessed be He!" Furthermore three times a day the devout Jew had to repeat the Shemoneh Esreh, the famous eighteen prayers called Eulogies, every one of which begins, "Blessed be You, O God." God was indeed, The Blessed One, (‘eulogetos'), the One who was continually blessed. And yet the very mouths and tongues with which they frequently and piously blessed God, were the very same mouths and tongues with which they cursed their fellowmen. James found this quite unacceptable. He considered it as unnatural as for a spring to gush out both fresh and salt water or a tree to bear opposite kinds of fruit.
But note that it is man who is unable to tame the tongue (see also James 3:14-15). Once God steps into the equation things are very different (James 3:13; James 3:17-18). See also Ephesians 4:29-31, ‘let no evil communication come out of your mouths but only such as is good for edifying, as fits the occasion, that it may impart grace to those who hear --- let all bitterness, and wrath, and anger, and clamour and slander be put away from you, with all malice, and be kind to one another, tender-hearted, forgiving one another, as God in Christ forgave you.'