1st century Christians were most likely Jews. Since Jews do not have a temple they do not perform sacrifices or offerings which cased in 70AD. There is not temple, no offering as their beliefs dictates that this can be done only in the temple. It is actually forbidden to make offering elsewhere. Therefore, Jews believe repentance for and of their own, individual sins directly to G-d (Hosea 14:2). For Jews back then and today; there cannot be mediator between you and G-d. Therefore, no need for Jesus. You are responsible for your own sin, not for sin anyone else. This is one of the central teaching of Judaism.
Slidin fast, when I was with WT, the entire concept of the Christ sacrifice never made sense. The original sin, being imperfect due Adam and Eve, etc.