Lead me in thy truth, and teach me: for thou art the God of my salvation; on thee do I wait all the day. —Psalm 25:5
The old Jewish believers of pre-Christian times who gave us the (to modern Protestants little-known) books, the Wisdom of Solomon and Ecclesiasticus, believed that it is impossible for an impure heart to know divine truth.
For into a malicious soul wisdom will not enter; nor dwell in the body that is subject unto sin. For the holy spirit of discipline will flee deceit, and remove from thoughts that are without understanding, and will not abide when unrighteousness cometh in.
These books, along with our familiar book of Proverbs, teach that true spiritual knowledge is the result of a visitation of heavenly wisdom, a kind of baptism of the Spirit of Truth which comes to God-fearing men.
This wisdom is always associated with righteousness and humility and is never found apart from godliness and true holiness of life. POM083-084
We need to learn that truth consists not in correct doctrine, but in correct doctrine plus the inward enlightenment of the Holy Spirit. POM084