Midrash Rabbah Leviticus on Stringing Together Words of Scripture

"Ben Azzai was sitting and expounding Scripture while a great fire was blazing all around him. Later, his students asked him about the incident: 'Is it perhaps that you have been delving into the arrangements of the Merkavah?' He replied to them: 'No. Rather, I string together passages from the Torah with passages from the Nevi'im, and passages from the Nevi'im with passages from the Ketuvim, and thus the words of Torah were as joyous as they were on the day they were given at Mount Sinai."

-- Midrash Rabbah Leviticus, 16.4


Here, Ben Azzai means that he is mapping out vibrational resonances between the various sections of the TaNaK. The indication is that this is a mystical activity that is similar in intensity to the Ma'aseh Merkavah when performed with skill.