The Old Testament is the Old Covenant of life under the Law. When Christ came, He established justification through grace, not the law--hence the New Covenant.\n\n"In that He says, “A new covenant,”  He has made the first obsolete. Now what is becoming obsolete and growing old is ready to vanish away." Hebrews 8:13
Why the Bible is splited in Testaments? why Testaments?