The Scriptures we call the Old Testament are valuable and powerful. The people who became the followers of Jesus only had those Scriptures and a few scattered letters and a few written testimonies that not all of them had access to for hundreds of years. Centuries. Twice as many centuries as the United States have seen.
Pharisees had memorized the old Scriptures. Jesus told some of them one day that those Scriptures were testifying about Him, leading them to Him so that they may receive Life:
The Father who sent Me has Himself testified about Me. You have not heard His voice at any time, and you haven’t seen His form. You don’t have His word living in you, because you don’t believe the One He sent. You pore over the Scriptures because you think you have eternal life in them, yet they testify about Me. And you are not willing to come to Me that you may have life.
(John 5:37-40 Holman Christian Standard Bible ©®)
Paul wrote to Timothy that those Scriptures were sufficient to lead someone to Christ:
But as for you, continue in what you have learned and firmly believed, knowing those from whom you learned, and that from childhood you have known the sacred Scriptures, which are able to instruct you for salvation through faith in Christ Jesus. All Scripture is inspired by God and is profitable for teaching, for rebuking, for correcting, for training in righteousness, so that the man of God may be complete, equipped for every good work.
(2 Timothy 3:14-17 Holman Christian Standard Bible ©®)
When Paul wrote that all Scripture is inspired, he was not referring to the New Testament, which did not yet exist. That does not mean that it is not also true about those Scriptures, but is one more reminder that the Old Testament Scriptures are valuable and powerful.
Do read them.