Why should we serve Hashem b'Simchah?
Rashi: Know that Hashem is Elokim, when He pays reward for your deeds. Idolaters should not serve b'Simchah, for [idols] do not pay reward.
Radak: Your Avodah should not be a burden, rather, b'Simchah with a good heart.
Radak citing Shocher Tov #1: It says "Ivdu Es Hashem b'Yir'ah" (2:11), and "Ivdu Es Hashem b'Simchah." How do we resolve these? When you pray to Hashem, your heart should be happy that you pray to Hashem, that there is no one like him among the gods. Perhaps this is without fear? "Ivdu Es Hashem b'Yir'ah" [refutes this].
Radak citing Shocher Tov #1: "Ivdu Es Hashem b'Yir'ah" in this world; in the future, flatterers will be gripped with trembling, and you will rejoice over the trembling that I will bring on the Nochrim.
Mesilas Yesharim (Perek 19): Simchah is a great primary fundamental in Avodah.
Malbim: There is a difference between serving Hashem and serving people. One who serves people is not happy in his Avodah, for he is not sure that he will receive reward. Even if he does receive reward, it is not together with the Avodah, rather, afterwards. He works sadly before he attains the purpose. Avodas Hashem itself is the reward and purpose; it is b'Simchah.
Why does it say "Bo'u Lefanav bi'Rnanah"?
Malbim: One who comes in front of a person to request something comes crying and screaming. Only his exit is with singing, if [the person] fulfilled his request. One who comes in front of Hashem to request comes with singing, for He will surely fulfill his request. 1
Malbim (Melachim I, 8:39) explained that Shlomo prayed that a Yisrael's request in the Mikdash not be granted if it will cause him to depart from fearing Hashem! Why didn't he say here that one knows that if his request would benefit him, Hashem will fulfill it? (PF)
