Sertillanges begins chapter two ("the virtues of the intellect") in Augustinian fashion, by identifying personhood with love: one is what one loves (or phenomenologically, one becomes what one loves). Intellectuals are (or ought to be) lovers of Truth, and therefore servants to Truth, and therefore submissive to Truth's commands.
Submission requires an active directing of passions and moral habits. They must be conformed to the demands that the love of Truth requires. Because of this, Virtue is necessary to the intellectual life as a purifier of the soul-in-service-to-Truth.
The particular virtues that aid intellectual pursuit include studiousness. Studiousness may be understood as diligent continuance of thought directed toward a question of truth. Temperance of mind is another virtue of the intellectual life. Temperance avoids the sloth of negligence as well as the pride of vain curiosity. Temperance aids the soul in avoiding taking up too little (malnourishment) or taking on too much (gluttony).
The vehicle of virtue is prayer. Indeed, prayer may be considered both a propaedeutic to study as well as the vessel by which the Spirit conveys the intellect to the Truth. To arrive at Truth is to arrive at God, the fount, headspring, source. The intellectual comes to the Truth through the effulgence of truths and this requires the humble acknowledgment of Truth as God's own to give, and it requires the humility to ask and receive wisely and freely.
The humility of prayer extends to the body. The body is our own unique tool and charge in the pursuit of Truth. The health and vitality of the body must be maintained to elicit the health and vitality of the mind, and it is often through the body that the mind is able to receive Truth.
For instance, think about the importance of memory for the receipt and retention of Truth. With music one must keep in the memory those notes that have passed out of hearing in order to understand, anticipate, and appreciate the notes that follow. One of the cultivators of memory is the body. Consider the difference of trying to memorize who my "riding partners" by repeating over and over again in the mind their names, as opposed to remembering them by riding with them once and then being responsible to remember them for the next time. The bodily experience of taking a trip together lends itself to the mind more potently than the abstraction of repeated names.
Love, studiousness, temperance, prayer, and bodily care constitute the chief virtues of the Intellectual Life.