I've heard of people who argue that the words of the Psalms were just David's thoughts; his questions, his ideas, his praises and prayers to God. Have you heard someone question Scripture in this way? Perhaps they will say the same thing of Solomon's wisdom in the Proverbs, or even Paul's letters in the New Testament. But the argument is that these words are merely the words of the human author, and therefore cannot be taken as the very word of God.
Let's briefly use the Psalms as an example. The New Testament clearly teaches us that we can trust the Psalms as the word of God. Consider the following evidence:
1. Jesus himself said that David wrote 'in the Spirit.' Jesus was quoting Psalm 110 to the Pharisees when he asked them, "How is it then that David, in the Spirit, calls him Lord..." (Matthew 22:43).
2. Peter the Apostle quoted from Psalm 69 and said, "Brothers, the Scripture had to be fulfilled, which the Holy Spirit spoke beforehand by the mouth of David..." (Acts 1:16). Here the words of David are attributed to the Holy Spirit! Clearly then, the Psalms are not to be taken lightly as David's thoughts that may or may not be true. The Psalms are the words of the Holy Spirit!
3. The early church, in a prayer to God during persecution, quoted from Psalm 2, and said, "...who through the mouth of our father David, your servant, said by the Holy Spirit..." (Acts 4:25). The early church understood that David's words were from the Holy Spirit.
So we see that we can trust God's word.
It is a wonderful truth that, "...no prophecy was ever produced by the will of man, but men spoke from God as they were carried along by the Holy Spirit" (2 Peter 1:21, ESV).