Tzava'at Harivash 51

I.e., with all your strength and energy. Cf. Eruvin 54a, that for Torah-study to be effective and retained one must clearly utter the words with the mouth. Moreover, one’s whole being should be involved, for “if it is ‘ordered’ in your 248 limbs it will be secure, but if not it will not be secure.”

All mitzvot must be performed with joy (see above, sect. 44, and note 3 there). This applies even more so to Torah-study, as explained below, sect. 119.

“Alien thoughts” relates to any kind of sinful, idle or distracting thoughts. Intensive and joyful Torah-study helps to overcome these, as it is said, “He who takes to heart the words of Torah will have negated for himself many mental preoccupations.. foolish preoccupations, unchaste preoccupations, preoccupations with the yetzer hara . . . preoccupations with idle things.” (Avot deR. Nathan, ch. 20) “Our sages thus declared that man should direct his mind and thoughts to the words of Torah and enlarge his understanding with wisdom, for unchaste thoughts prevail only in a heart devoid of wisdom.” (Maimonides, Hilchot Issurei Bi’ah 22:21, based on Kidushin 30b and Midrash Mishlei, ch. 24).