+Jn 12: 44-50
Jesus cried out and said, “Whoever believes in me believes not only in me but also in the one who sent me,
and whoever sees me sees the one who sent me.
I came into the world as light, so that everyone who believes in me might not remain in darkness.
And if anyone hears my words and does not observe them, I do not condemn him, for I did not come to condemn the world but to save the world.
Whoever rejects me and does not accept my words has something to judge him: the word that I spoke, it will condemn him on the last day,
because I did not speak on my own, but the Father who sent me commanded me what to say and speak.
And I know that his commandment is eternal life. So what I say, I say as the Father told me.”
The New American Bible
The Catechism of the Catholic Church
LIVING IN THE TRUTH
2465 The Old Testament attests that God is the source of all truth. His Word is truth. His Law is truth. His “faithfulness endures to all generations.” Since God is “true,” the members of his people are called to live in the truth.
2466 In Jesus Christ, the whole of God’s truth has been made manifest. “Full of grace and truth,” he came as the “light of the world,” he is the Truth. “Whoever believes in me may not remain in darkness.” The disciple of Jesus continues in his word so as to know “the truth [that] will make you free” and that sanctifies. To follow Jesus is to live in “the Spirit of truth,” whom the Father sends in his name and who leads “into all the truth.” To his disciples Jesus teaches the unconditional love of truth: “Let what you say be simply ‘Yes or No.'”
2467 Man tends by nature toward the truth. He is obliged to honor and bear witness to it: “It is in accordance with their dignity that all men, because they are persons . . . are both impelled by their nature and bound by a moral obligation to seek the truth, especially religious truth. They are also bound to adhere to the truth once they come to know it and direct their whole lives in accordance with the demands of truth.”
2468 Truth as uprightness in human action and speech is called truthfulness, sincerity, or candor. Truth or truthfulness is the virtue which consists in showing oneself true in deeds and truthful in words, and in guarding against duplicity, dissimulation, and hypocrisy.
2469 “Men could not live with one another if there were not mutual confidence that they were being truthful to one another.” The virtue of truth gives another his just due. Truthfulness keeps to the just mean between what ought to be expressed and what ought to be kept secret: it entails honesty and discretion. In justice, “as a matter of honor, one man owes it to another to manifest the truth.”
2470 The disciple of Christ consents to “live in the truth,” that is, in the simplicity of a life in conformity with the Lord’s example, abiding in his truth. “If we say we have fellowship with him while we walk in darkness, we lie and do not live according to the truth.”