According to Devarim 4:2 (and 13:1), there are to be no additions to the Torah ('Do not add to what I command you and do not subtract from it, but keep the commands of the Lord your God that I give you . . . All this word which I command you, that shall you observe to do; you shall not add thereto, nor diminish from it') In light of that, how are the feasts of Purim and Hanukkah, two additional feasts, justified? Even further, Shemini Azeret and Simchat Torah?