Compare Matthew 7:16. James is saying that it is inconsistent with a believer's character and identity in Christ to use the tongue for sin.
The tongue was given to be used with dignity, honor, and respect (Matt. 12:35; cf. Prov. 10:20-21). It is meant to proclaim the life-changing message of salvation (Rom. 10:14-15). A fitly spoken word (Prov. 25:11-12; cf. Prov. 15:23) may be applied by the Spirit for sanctification (John 17:17). Words should be used for healing (2 Cor. 7:5-7; Col. 4:6). The tongue has the power of worship (Heb. 13:15). Our tongues are meant for the glory of God in all things (1 Cor. 10:31; Col. 3:17; 1 Pet. 4:11). "Oh, magnify the LORD with me, and let us exalt his name together!" (Psa. 34:3). Hughes says:
First, we must ask God to cauterize our lips, confessing as Isaiah did, "Woe to me! I am ruined! For I am a man of unclean lips, and I live among a people of unclean lips, and my eyes have seen the King, the Lord Almighty" (Isaiah 6:5). Then we need to submit to the cleansing touch: "Then one of the seraphs flew to me with a live coal in his hand, which he had taken with tongs from the altar. With it he touched my mouth and said, See, this has touched your lips; your guilt is taken away and your sin atoned for" (Isaiah 6:6, 7). Next we can prepare to serve: "Then I heard the voice of the Lord saying, Whom shall I send? And who will go for us? And I said, Here am I. Send me" (Isaiah 6:8). Isaiahs outline as a spiritual exercise, performed with all ones heart, will work wonders in our lives! Let us all do this today!
Second, hand-in-hand with the first step, there must be an ongoing prayerfulness regarding our tongues regular, detailed prayer. This, coupled with the first step, will work a spiritual miracle.
Third, we must resolve to discipline ourselves regarding the use of the tonguenot to criticize, not to give or receive gossip, not to belittle or demean or falsely flatter, not to lie, not to boast.
The tongue, so tiny, is immensely powerful. Four reporters, good old boys, having a few beers in a Denver bar in 1899 provided the specious spark that ignited the infamous Boxer Rebellion. The tongue is indeed mightier than generals and their armies. It can fuel our lives so they become fiery furnaces, or it can cool our lives with the soothing wind of the Spirit. It can be forged by Hell, or it can be the tool of Heaven.
James concludes his section on wise speech with several more illustrations that amplify the hypocrisy of using the tongue for both blessing and cursing the image of God.
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. These observations from nature are designed to jolt readers to attend to their speech, if they want to grow in wisdom.