Rashi on Deuteronomy 32:46/רש"י על דברים ל״ב:מ״ו

1שימו לבבכם SET YOUR HEARTS [UNTO ALL THE WORDS WHICH I TESTIFY AGAINST YOU THIS DAY] — Indeed, it is necessary for a man that his eyes, his heart and his ears, should all be attentively directed to the words of the Torah, for so it states, (Ezekiel 40:4) “Son of man, behold with thine eyes, and hear with thine ears, and set thine heart [upon all that I shall show thee]” (viz., the plan of the Temple). If in the case of the model of the Temple, which was being made visible to the eyes and was being measured by a rod, it was necessary for a man, according to Scripture, that his eyes, his ears and his heart be attentive, then in order to understand the words of the Torah which are like mountains suspended on a hair (i.e., numerous laws are derived from a single word of the Torah), how much the more is this necessary!