חסידות אויף שיר השירים 1:9

If a person is praying and has a thought that is extraneous to the words of prayer, this means that the external husks of evil are riding upon the words of his speech, God forbid. This is the meaning of the verse,¹⁰⁵Song of Songs 1:9 “I have compared you (Deemeteech-דמיתיך), my beloved, to My horse in Pharaoh’s chariots.” That is, words are called “horses”¹⁰⁶(See Tikkunei Zohar, Tikkun 47, 84b, and elsewhere.) because they carry meaning and intention, just like a horse carries its rider. When Pharaoh, which refers to the extraneous thought, rides upon speech, then, “I have silenced you (Deemeeteech-דמיתיך), my beloved.”¹⁰⁷The word Deemeeteech-דמיתיך also means, “be silent.” In other words, you would be better off to be silent. In contrast, “Words that come from the heart enter the heart,”¹⁰⁸Sefer HaYashar, Ch. 13 meaning that they enter the “upper heart” by means of the intellect,¹⁰⁹See Shaar HaYichud of Rabbi DovBer of Lubavitch, Ch. 37, translated as The Gate of Unity. as known.

If you pray while holding another thought in mind, it is as if - God forbid! - the klippot, the rough husks of reality are riding along on your words. Because Thought rides on Speech, and this is the meaning of (Song of Songs 1:9) "To a horse in Pharaoh's chariots -" speech is likened to horses, and when Pharaoh (that is, the foreign thought) rides upon them, then "I have likened you, my beloved." It would be far better to be silent. Yet what comes from the heart enters the heart, to the supernal heart by means of breath, as is well known.