Contradiction with Proverbs 27:2
Acts 26:4 mentions Paul speaking about his own manner of life, while Proverbs 27:2 advises letting another person praise you, not your own mouth.
Proverbs 27:2: Let another man praise thee, and not thine own mouth; a stranger, and not thine own lips.
Contradiction with Matthew 6:1
In Acts 26:4, Paul is talking about his past openly, whereas Matthew 6:1 warns against performing acts of righteousness to be seen by others.
Matthew 6:1: Take heed that ye do not your alms before men, to be seen of them: otherwise ye have no reward of your Father which is in heaven. [alms: or, righteousness] [of your: or, with your]
Contradiction with 2 Corinthians 10:18
Acts 26:4 involves Paul giving testimony about his own life, yet 2 Corinthians 10:18 states that the one who commends themselves is not approved, but the one whom the Lord commends.
2 Corinthians 10:18: For not he that commendeth himself is approved, but whom the Lord commendeth.
Contradiction with Jeremiah 9:24
Acts 26:4 features Paul recounting his past, while Jeremiah 9:24 emphasizes that one should boast only in understanding and knowing the Lord, not in their own past.
Jeremiah 9:24: But let him that glorieth glory in this, that he understandeth and knoweth me, that I [am] the LORD which exercise lovingkindness, judgment, and righteousness, in the earth: for in these [things] I delight, saith the LORD.
Contradiction with Philippians 3:7
Acts 26:4 implies Paul reflecting on his former life, but Philippians 3:7 states that Paul regards whatever was gain to him in his past life as loss for Christ.
Philippians 3:7: But what things were gain to me, those I counted loss for Christ.
Contradiction with Isaiah 64:6
Acts 26:4 involves Paul sharing his life history with others, whereas Isaiah 64:6 indicates all our righteous acts are like filthy rags and should not be boasted about.
Isaiah 64:6: But we are all as an unclean [thing], and all our righteousnesses [are] as filthy rags; and we all do fade as a leaf; and our iniquities, like the wind, have taken us away.