The Mitteler Rebbe explains: the joy of a mitzva is the delight in performing the mitzva and having done Hashem’s Will. This joy made the AriZal worthy of Divine inspiration. It follows that although in these later generations we are completely lacking the G-dly light of love and fear of Hashem that Jews had previously, and we only have the physical mitzvot and the joy in doing them. Nevertheless, we can reach higher levels than they did. And this joy creates the Crown of Moshiach.