L'Hamtik haDaf by RPML: Brachos 31b

Brochas: 31b

Mishna: One should not rise to pray (shemone esre) other than with an attitude of "coved rosh" (seriosness/reverence).

Gemara: From where (do we know) this? ...R. Nachman bar Yitzhak said: Serve Hashem with "yira" (awe), and "gilo" (rejoice) with trepidation (Psalms 2:11)

The Bach (Orach Chaim 93)interprets the Gemara as suggesting that the preferable state of mind is awe. Failing that, one should have "simcha" (joy) rather than "s'chok" (levity).

The Maharal (Netzach Yisrael 23) prefers an approach which suggests that there is no dichotomy between reverence and joy when it comes to tefillah.

The requirement of reverence is a function of Chorban Beis haMikdash, the destruction of the Temple. We need to recognise that the world has lost something fundamental and that unless there is a serious recognition of this fact, we cannot legitimately aspire to a restitution of the status quo ante. As such, the quality of our current interaction with Hashem which has become flawed due to the loss of the Beis haMikdash, is dependent upon a certain seriousness/reverence of approach, facilitated by a recognition that we are created beings addressing our creator, an awareness of which should inspire the appropriate level of awe.

At the same time, a feeling of joy is completely appropriate. It stems from an understanding based on precisely the same factor that inspired awe, namely that we are created beings addressing our creator. This makes us into servants addressing our master. And of course, there exists the strongest of bonds in this master/servant relationship, such that the quality of that relationship should cause us to rejoice.

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