19 Since then the Body of Christ is in the end to be severed in body also from the unholy and wicked, but now meanwhile groans among them, what does the “love of Christ among the daughters, as the lily among thorns”? What are her words? What her conscience? What is the “appearance of the king's daughter within”? Lo, hear what she says. “Prove me, O God, and know my heart”. Do Thou, O God, Thou prove me, Thou know; not man, not an heretic, who neither knows how to prove, nor can know my heart, whereas You prove, and know that I consent not to the deeds of the wicked, while they think that I can be defiled by the sins of others; so that, while I in my long wandering do what I mourn in another Psalm, that is, while I “labour for peace among them that hate peace,” until I come to that Vision of peace, which is called Jerusalem, “which is the mother of us all,” the city “eternal in the heavens;” they, contending, and falsely accusing and separating themselves, may “receive,” not, evidently, in eternity, but “in vanity, their cities.” Why this? Observe what follows.
20. “And see,” says he, “if there be any way of wickedness in me, and lead me in the way everlasting”. “Search,” he says, “my paths,” that is, my counsels and thoughts. What else says he, but “lead me in Christ”? For who is “the way everlasting,” save He that is the life everlasting? For everlasting is He who said, “I am the Way, and the Truth, and the Life.” If then you find anything in my way which displeases Your eyes, since my way is mortal, do Thou “lead me in the way everlasting,” wherein is no iniquity; for even “if any man sin, we have an Advocate with the Father, Jesus Christ the righteous; and He is the propitiation for our sins;” He is “the Way everlasting” without sin; He is the Life everlasting without punishment.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)