When one approaches a mitzvah, he must feel the greatest joy at the opportunity that he is offered with this mitzvah.

When completing the mitzvah, he should feel happiness at having achieved his goal.

But while he is actually doing the mitzvah, he must feel awe that is to be experienced by a mortal man while he is standing before a king. He must recognize that any wrong word or move could result in tragedy indeed! ~ R’ Shlomo Kluger zt”l