One scripture says, "Serve the Lord with joy." And another scripture says (Psalms 2:11), "Serve the Lord with fear." Rabbi Ibu said, "When you stand to pray, let your heart be filled with joy, for you are serving the Most High God." Another explanation of "serve the Lord with joy" is that it is possible to serve Him without fear. Therefore, the scripture emphasizes fear. Rabbi Acha said, "In this world, fear is necessary. But in the future (Isaiah 33:14), I will see trembling among the wicked. And the righteous will rejoice in trembling, as I have spoken about the nations."