As Jews we ALWAYS believed in the after-world that a) our souls live on after it leaves our physical body and b) there is a world-to-come, a time when the dead will be resurrected. These are clearly hinted to in the Torah. For example Genesis 47:30 “I will lie with my forefathers, and you shall carry me out of Egypt, and you shall bury me in their grave.” And he  said, “I will do as you say.”. And Exodus 16:1 “Then Moses and the children of Israel sang this song to the Lord…” from the future tense of the verse “Then Moses…” In the Hebrew language it says “Then Moses WILL sing” from which our Sages have learned “Then…Will..” in the future time, at the time of the coming of the Messiah.

There are certain accepted beliefs that were never written as they were not needed to be written just like it is not written that G-d in not a bodily form.

These basic and fundemental beliefs were specifies clearly in the 13 Principals of Faith compiled by Rabbi Moses Miamonodes (Rambam)