Psalm 151 is not in the Bible. While it is included in a couple versions of the Bible, such as the one used by the Greek Orthodox church, the source for the Psalm is not the Hebrew text. Instead, it’s from a Greek collection of works translated and collected between the third and first centuries BC. That was after the Jewish canon was closed, with Psalm 151 believed to be one of the Apocryphal writings. Because there is no evidence of it ever existing in the original canon and we recognize God’s sovereignty even over history, this Psalm is not canonical and should not be treated as part of the Bible. Although Psalm 151 is not canonical and some historical statements in it may be inaccurate, it does not contain anything that would be considered heretical. It can be read online at: Psalm 151 (CEB).
While scholarship and popular magazines regularly bring up “lost” works of Scripture, the biblical canon does not come from a council, church, or any other human organization. From a human standpoint, something might be accidentally lost or even intentionally suppressed,. but that cannot happen with true Scripture because it comes from God.
That does not mean that the Bible floated down from heaven. Rather,God worked in history to preserve His canon. The working of the Holy Spirit in believers and circumstantial events revealed the difference between true and false works. That does not mean Psalm 151 is necessarily bad. However, only true Scripture is profitable for the believer (2 Timothy 3:16–17). If God had wanted Psalm 151 in the canon then, just like he preserved the other 150 Psalms, He would have preserved this one, too. He did not and, therefore, we can be confident that He did not intend it to be a part of the Bible.
What does this mean? Regardless of what “lost text” scholarship finds or claims was wrongly excluded from Scripture, we can have confidence that it was not supposed to be part of the Bible. God is the one Who created everything out of nothing (Genesis 1), Who moves the hearts of kings to do as He wills (Proverbs 21:1; Ezra 1:1), and Who guided the tiniest details, such as a coin ending up in a specific fish’s mouth (Matthew 17:24-27). If this all powerful God wanted Psalm 151 in the Bible, it would never have been overlooked in the first place.