CATECHISM OF THE CATHOLIC CHURCH
SECOND EDITION

Paragraphs 214–217

214 God, "HE WHO IS", revealed himself to Israel as the one "abounding in steadfast love and faithfulness". These two terms express summarily the riches of the divine name. In all his works God displays, not only his kindness, goodness, grace and steadfast love, but also his trustworthiness, constancy, faithfulness and truth. "I give thanks to your name for your steadfast love and your faithfulness." He is the Truth, for "God is light and in him there is no darkness"; "God is love", as the apostle John teaches.
215 "The sum of your word is truth; and every one of your righteous ordinances endures forever." "And now, O LORD God, you are God, and your words are true"; this is why God's promises always come true. God is Truth itself, whose words cannot deceive. This is why one can abandon oneself in full trust to the truth and faithfulness of his word in all things. The beginning of sin and of man's fall was due to a lie of the tempter who induced doubt of God's word, kindness and faithfulness.
216 God's truth is his wisdom, which commands the whole created order and governs the world. God, who alone made heaven and earth, can alone impart true knowledge of every created thing in relation to himself.
217 God is also truthful when he reveals himself - the teaching that comes from God is "true instruction". When he sends his Son into the world it will be "to bear witness to the truth": "We know that the Son of God has come and has given us understanding, to know him who is true."