Early Christianity is the fulfillment of 1st Century Judaism with Jesus Christ being revealed as the Messiah and King. Modern day Judaism, that is Rabbinic Judaism (which followed some time after the destruction of the 2nd Temple) denies Jesus as that expected Messiah and has an expectation of someone else that is to come.
For Christians, The Old Testament and New Testament are very much coupled together. There's a lot of prophecies and typologies you can read about from the Old Testament that finds its fulfillment in Jesus and the New Testament (such as the suffering Messiah).
I'd suggest C.S. Lewis' book "Mere Christianity" (who was good friends and influenced to convert by J.R.R. Tolkien and G.K. Chesterton) to get a clearer picture of Christianity without the sugar coating we commonly get from the media today. Lewis brings up the Trilemma, which is unique only to the founder of Christianity.
For Christians, The Old Testament and New Testament are very much coupled together. There's a lot of prophecies and typologies you can read about from the Old Testament that finds its fulfillment in Jesus and the New Testament (such as the suffering Messiah).
I'd suggest C.S. Lewis' book "Mere Christianity" (who was good friends and influenced to convert by J.R.R. Tolkien and G.K. Chesterton) to get a clearer picture of Christianity without the sugar coating we commonly get from the media today. Lewis brings up the Trilemma, which is unique only to the founder of Christianity.