The Baal Shem Tov passed through a Jewish community before the High Holidays where they asked him to stay and pray with them. He inquired about the cantor who would lead the communal prayers. They told him that the cantor sang a lovely, cheerful song of his own for the confession of sins in the Yom Kippur prayer.

The Baal Shem Tov asked to bring the cantor before him, and demanded of him why he sang about sins against G‑d in a cheerful tune. Upon hearing his response, he resolved to stay in that place for the High Holidays

What did the cantor answer? He replied, “I am a launderer by profession, and here I have been asked to launder the clothes of the greatest King of kings. Should I not rejoice in my task?”

יחשוב כשמתפלל שבאותיות מתלבש השי״ת, פי׳ דאין אנו יודעים מה אדם חושב אא״כ ידבר, נמצא הוי הדיבור מלבוש למחשבה, ויאמר בלבו מלך גדול כזה אני עושה לו מלבוש, ראוי לי לעשות בשמחה. וידבר בכל כחו, כי מזה נעשה אחדות עמו ית', כי כחו בהאות ובהאות שורה הקב״ה, נמצא הוא אחדות עמו ית׳

When you pray, visualize that G‑d is invested within the letters of the prayers.

You see, words are clothing for thoughts. As fine clothes bring out a person’s inner beauty, so well-spoken words bring out your inner thoughts. They emerge from your personal world into the revealed world. So too, your words of prayer provide the same sort of clothing for G‑d’s presence.

If so, you should be thinking, “This is a great king, and I am making clothes for Him! If so, I should do this with joy!”

Put all your strength into those words, for this way you will attain oneness with Him. Since your energy is in your articulations of each letter, and in each letter G‑d dwells, in this way you have become one with Him.

—Tzava’at Harivash 108