Rabbi Steinsaltz writes:
It is told that once the Rabbi of Kotzk asked one of his pupils to tell him what he thinks of while praying.
The man began to tell the Rabbi about his thoughts during prayers — a very learned lecture about the unity of God in the higher world and in our world.
The Rabbi, who was a volcano of God-seeking and truth-seeking, and one of the greatest teachers on those subjects, could not suppress his anger any longer and cried: “And where is your stomach?” — meaning:
Where is your own prosaic self in all this high philosophy?
Where are you in this strange, cold, distant and impersonal exaltation?”
–Rabbi Adin Steinsaltz
From “Human Holiness” in The Strife of the Spirit by Rabbi Adin Steinsaltz