YHWH said, Since this people draw near me with their mouth, and with their lips do honor me, but have removed their heart far from me, and their fear toward me is taught by the precept of men (Isaiah 29:13).
“Rabbi Yirmiyahu said in the name of Rabbi Eli’ezer, ‘One who was reciting the Prayer and his concentration lapsed, if he knows that he can go back and concentrate, he should go back and recite the Prayer. And if not, he should not go back and recite the Prayer.’
Rabbi Ḥiyya the great said, ‘In all my days I never concentrated. One time I wanted to concentrate and I meditated. And I said to myself, ‘Who goes up first before the king? The Arkafta [a high dignitary in Persia] or the Exilarch?’
Shemuel said, ‘I count the birds [or: clouds].’
Rabbi Bun son of Ḥiyya said, ‘I count rows of bricks.’ Rav Matanyah said, ‘I consider myself lucky. For when I reach the Thanksgiving blessing, my head bows instinctively’” (JT Berakhot 2:4, 5a).
“What difference does it make to the blessed Holy One whether one slaughters an animal from the neck or from the throat [as Halakhah dictates]? The mitsvot were given only to purify people” (Bereshit Rabbah 44:1).
“There is service of the blessed Holy One based on activity of the body, and this is considered service. Then there is service of the blessed Holy One that is more internal, and this is essence, for all depends on that inner service, essence of all” (Zohar 2:201a).
“[One] talks with people and is occupied with his bodily necessities while his intellect is wholly turned toward Him, may He be exalted, so that in his heart he is always in His presence, may He be exalted, while outwardly he is with people” (Maimonides, Guide of the Perplexed 3:51).