Psalm 12 is coming from a very disturbed heart, where the speaker doesn't know how to deal with the abundance of evil-speaking people and the loss of righteous people.
The speaker thinks that he's stuck in a world where godly people are disappearing and shriveling up like a dried-out harvest. The people who surround the speaker are braggers and flatterers that like to deceive others (Making a mental note to myself--personal confidence and outgoing compliments are good, but personal vanity and flattering others=bad). But God will eliminate the communications of people whose speech only accomplishes wrong things.
Verse 4 shows the cruel people claiming power over their own speech and wondering why anyone would try to stop them from saying their piece. But God will stop them, because they use their words to oppress the needy and to harm the poor. God always defends the helpless against the proud.
And in verse 6 we learn that, just as the words of the evil people are corrupt and cause only harm, God's words are totally purified and bring only goodness.
I guess it just goes to show that words, whether written or spoken, can hold the power of life and death. We should be careful with the way we use ours, always.
1Help, Lord; for the godly man ceaseth; for the faithful fail from among the children of men.
2 They speak vanity every one with his neighbour: with flattering lips and with a double heart do they speak.
3 The Lord shall cut off all flattering lips, and the tongue that speaketh proud things:
4 Who have said, With our tongue will we prevail; our lips are our own: who is lord over us?
5 For the oppression of the poor, for the sighing of the needy, now will I arise, saith the Lord; I will set him in safety from him that puffeth at him.
6 The words of the Lord are pure words: as silver tried in a furnace of earth, purified seven times.
7 Thou shalt keep them, O Lord, thou shalt preserve them from this generation for ever.
8 The wicked walk on every side, when the vilest men are exalted.