Musar su Salmi 2:11

And this is what is meant: "Serve the Lord with fear" (Ps. 2:11) — the fear of losing His love" and rejoice with trembling out of this great fear of losing the love of the Creator, rejoice that you have the opportunity to do His will.

When he contemplates all of this, it will be impossible for his heart to not fear and for him to not quiver while he speaks his words before Him, blessed be He, and utters His Name, and strives to find His favor. This is what scripture says: "Serve G-d with fear, and rejoice in trembling" (Tehilim 2:11), and "G-d is revered in the great council of the holy ones and feared by all around Him"(Tehilim 89:8).

We thus see that, one must not judge the piety of an act by itself alone. Rather, one must view it from all angles that human intellect can foresee before he can truthfully judge whether it is better to do it or to abstain from it.

Likewise our sages, of blessed memory, said regarding the Levites: "because they knew that whoever carries the Ark merits great reward, they abandoned the Shulchan, Menorah and Altars, and all ran to the Ark to gain reward. Then, this person argued saying 'I will carry it from here' and that person argued saying 'I will carry it from here' until they came to lightheadedness and the Divine presence would hit them..." (Midrash Raba 5:1).

There are two diametrically opposed verses, each one of which purports to tell us how to serve the Lord by prayer. In Psalms 100,2 we are told: עבדו את ה' בשמחה, "Serve the Lord in joy," whereas in Psalms 2,11 we are told: עבדו את ה' ביראה, "Serve the Lord in trepidation, reverence!" The plain meaning of the verses in question is that they apply to prayer which is called עבודה שבלב, "service with the heart." Our sages have said that while praying, we must direct our heart toward Heaven and our eyes towards Earth: Our downcast eyes to remind us of our puniness, our insignificance before G–d the Exalted. Our uplifted heart will induce fear and trepidation so that we may serve the Lord out of true reverence. Once we have attained this level of reverence our heart will contemplate what is above us and thus will be full of joy that we have been found fit to serve such a Master. We note that both emotions are an integral part of prayer.

What is meant here is something that I have explained elsewhere in connection with the verses 1) "Serve the Lord with joy!" (Psalms 100,2), and 2) "Serve the Lord with fear!" (Psalms 2,11). When a person gets ready to pray he should consider that he is totally insignificant, no more than a drop of evil-smelling semen, sinful and obstinate and thus he will become fearful and feel ashamed. Hence his eyes will be turned downward. After that he should contemplate the greatness of the Lord, how exalted G–d is, etc. These feelings will produce joy within him. Joshua son of Nun was of the tribe of Ephrayim. We find that G–d had granted both Moses and Joshua the attributes of חכמה, and that both of them prostrated themselves when praying. Our sages, pointing to the example of Joshua, are on record that any scholar who is not certain that his prayer will find a favorable response must not prostrate himself when praying.