Both are important to the understanding of the word of God -- the reason is because the New Testament answers many of the questions and mysteries, the promises that God makes, that are posed in the Old Testament. For example, Jesus' birth was prophesied hundreds and thousands of years before his birth -- it would discredit the fulfillment of scripture and very proof of the existence of God, if someone were to exclude the Old Testament scriptures from their understanding of Christianity.

@clouds

that’s a good point. Thank you. Ya I also think that God gives us both Old Testament and New Testament for a reason. We shouldn’t say either is not important 

I was wondering this too! Today I stopped by the Dollar Store and saw that they had New Testament Bibles (without the Old Testament).

That's so sad, I hope that they realize that only selling the New Testament would leave new believers especially mislead and confused, and for old believers, I'm sure if they didn't know about the importance of the Old Testament, they would also be confused.

I dont think it's okay to read only the New Testament because the New Testament references the Old Testament a lot. I'm not sure if it would be possible to understand the New Testament without the Old Testament.