Isaiah 6:5 (ESV)
⁵  And I said: “Woe is me! For I am lost; for I am a man of unclean lips, and I dwell in the midst of a people of unclean lips; for my eyes have seen the King, the LORD of hosts!”

When Isaiah sees the holy God in a dramatic vision he equates his sin with his lips.  How often are my words — both the outer words we hear and the inner ones i speak in my heart — one of my weakest places of failure and sin.

James 3:5-8 makes it very clear — anything that is powerful can be a great source of giving life or an explosive way of destroying life.  I can sing out in worship of God but then contaminate myself and others when I use my same tongue to tear down a person bearing the image of God.  I think that is why if you speak in an attacking way to one of my children you are likely to get me in your face… they are my image bearers — to attack them is to attack me.  God takes the words we use about people he has created very seriously.

In James and Isaiah fire shows up — the tongue can be like a small fire that sets loose a destructive forest fire — but God can also touch and cleanse the unclean lips with his merciful fire.

When God is maturing a leader — he will never leave out the tongue.