Daniel purposed in his heart that he would not defile himself with the portion of the king's delicacies, nor with the wine which he drank; therefore he requested of the chief of the eunuchs that he might not defile himself. Daniel 1:8, NKJV. BLJ 294.1
The human intellect must gain expansion and vigor and acuteness and activity. It must be taxed to do hard work, or it will become weak and inefficient. Brainpower is required to think most earnestly; it must be put to the stretch to solve hard problems and master them, else the mind decreases in power and aptitude to think. The mind must invent, work, and wrestle, in order to give hardness and vigor to the intellect; and if the physical organs are not kept in the most healthful condition by substantial, nourishing food, the brain does not receive its portion of nutrition to work. BLJ 294.2
Daniel understood this, and he brought himself to a plain, simple, nutritious diet, and refused the luxuries of the king's table. The desserts which take so much time to prepare are, many of them, detrimental to health. Solid foods requiring mastication will be far better than mush or liquid foods. I dwell upon this as essential.... BLJ 294.3
The intellect is to be kept thoroughly awake with new, earnest, wholehearted work. How is it to be done? The power of the Holy Spirit must purify the thoughts and cleanse the soul of its moral defilement. Defiling habits not only abase the soul, but debase the intellect. Memory suffers, laid on the altar of base, hurtful practices.... BLJ 294.4
When teachers and learners shall consecrate soul, body, and spirit to God, and purify their thoughts by obedience to the laws of God, they will continually receive a new endowment of physical and mental power. Then will there be heart-yearnings after God, and earnest prayer for clear perception to discern.... BLJ 294.5
Diligent study is essential, and diligent hard work.... A well-balanced mind is not usually obtained in the devotion of the physical powers to amusements. Physical labor that is combined with mental taxation for usefulness is a discipline in practical life, sweetened always by the reflection that it is qualifying and educating the mind and body better to perform the work God designs us to do in various lines.... The mind thus educated to enjoy physical taxation in practical life becomes enlarged and, through culture and training, well disciplined and richly furnished for usefulness, and acquires a knowledge essential to be a help and blessing to themselves and to others.—Fundamentals of Christian Education, 226-229. BLJ 294.6