Contradiction with Proverbs 12:22
Galatians 1:20 emphasizes truthfulness, whereas Proverbs 12:22 highlights that lying lips are an abomination, contradicting any assertion that might include falsehood.
Proverbs 12:22: Lying lips [are] abomination to the LORD: but they that deal truly [are] his delight.
Contradiction with Exodus 20:16
While Galatians 1:20 underlines telling the truth, Exodus 20:16 prohibits bearing false witness, creating a contrast if truth is not upheld.
Exodus 20:16: Thou shalt not bear false witness against thy neighbour.
Contradiction with John 8:44
Galatians 1:20 asserts truth, but John 8:44 describes those deceitful like the devil, providing a contrasting moral example.
John 8:44: Ye are of [your] father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it. [of his own: or, from his own will or disposition]
Contradiction with Titus 1:2
Galatians 1:20 states a truth, paralleling Titus 1:2, which refers to God's impossibility to lie, thus contrasting human capability to deviate from truth.
Titus 1:2: In hope of eternal life, which God, that cannot lie, promised before the world began; [In: or, For]