The Old Testament is the inspired Word of God, and we are to learn lessons from it, as God taught them through His interactions with His Chosen People. The New Testament is also inspired by God, but it's more contemporaneous, because it's written fairly soon after Jesus's Death, Resurrection, and Ascension, and the major parts are written by His Disciples, or men who were disciples of His Disciples, so there hadn't been a long passage of time before it was written.
Really? What part have you found in error?