Psalm 12 - Overcomer - Help, Lord, for the godly ceases
This is the 7th Psalm for the Overcomer. To be an overcomer, we need to have this attitude toward the world, which includes the religious Christian world. The Lord's word which we have stored up in us must be purified many times.
This Psalm is also "upon the 8th". There are only 2 Psalms upon the 8th, this Psalm and Psalm 6. The only other place "the 8th" is used in 1 Chron 15:21 when the Levites sung songs celebrating David's bringing the ark to Jerusalem. I think this means that they sung Psalms 6 & 12 in bringing the ark to its place. Psalm 6 "Lord, in wrath rebuke me not", applies to David's 1st attempt to bring back the ark, which was disastrous because he had not followed the Lord's way in His word (1 Chron 13; Num 4:15-19; 15:2). Psalm 12 extols the Lord's word (vv 6-7), and may express David's wonder that no one else was burdened to actually bring the ark to its place. They would talk a lot about it, but do nothing.

It is easy to get deluded in vanity. Mixing the Lord's words with faith saves us from vanity (Heb 4:2). God's word becomes to us both richer and purer. When we trust in the Lord and believe that He must honor His word, we become the furnace of earth in which the Lord tries His word over and over. His word becomes more precious in us each time.

It is easy for the Lord's word among us to become mixed with myths. We should speak truth each one with his neighbor, meeting in our homes (Eph 4:17,25).  It is good to ask eachother, does the Lord's word really say that? The important truths we believe and stake our life upon must be founded directly upon the Word, not upon the trust in the understanding of a servant of the Lord, no matter how greatly that servant has been used by God. We should appreciate the Lord's servant for helping us see the truth in the Word, but we believe it because the Word says it.

v6 lit. The words of the LORD are pure words, silver tried in a furnace for earth, 7 times purified.
It doesn't actually mean "furnace of earth" as in KJV because of the preposition le prefixed to "earth". le means "to", "for" or "through". So the Lord's word is purified for benefit of the earth and by means of the earth.