Hebrews 8:6 (NKJV)
What if somehow you mistakenly were receiving emails or text messages that were meant for another person, what would you do? Would you just keep reading the emails or messages and begin a correspondence with the other person and maybe start asking for their advice? Most people in a situation like this would reply and let the sender know that they somehow have the wrong person. This other person may be very nice and even have some encouraging or helpful things to say but those things were not really meant for you, those things were written for someone else.
Today, because of Jesus, we have a new covenant with God. Through His death on the cross Jesus opened the way for all mankind to have access to God; now we just need to put our confidence in the work of Jesus and be born again. In the Bible we have the Old Testament, the old covenant, and the New Testament, the new covenant. Jesus came to bring us this new and better covenant. It is vital that Christians become familiar with and base their life primarily on the New Testament, the new covenant. This is not to say that we completely reject the Old Testament, but we must realize that the New Testament was written directly to us.
Under the old covenant no one could be born again and have their sins washed away as we have in the new covenant. We have a completely different relationship with God than the people in the Old Testament had. The Old Testament was written to give us natural examples of the spiritual truth that we find in the New Testament. If we do not spend the majority of our time with the New Testament we may develop an inaccurate view of our relationship with God and what belongs to us today as Christians. To fully live out the life that God has provided for us through Jesus we need to live in the New Testament, that is what was written to us!