"The Word of Wisdom was "given for a principle with promise" (D&C 89:3). That word principle in the revelation is a very important one. A principle is an enduring truth, a law, a rule you can adopt to guide you in making decisions. Generally principles are not spelled out in detail. That leaves you free to find your way with an enduring truth, a principle, as your anchor.  Members write in asking if this thing or that is against the Word of Wisdom. It's well known that tea, coffee, liquor, and tobacco are against it. It has not been spelled out in more detail. Rather, we teach the principle together with the promised blessings. There are many habit-forming, addictive things that one can drink or chew or inhale or inject which injure both body and spirit which are not mentioned in the revelation.  Everything harmful is not specifically listed; arsenic, for instance-certainly bad, but not habit-forming! He who must be commanded in all things, the Lord said, "is a slothful and not a wise servant" (D&C 58:26)."  -Boyd K. Packer, "The Word of Wisdom: The Principle and the Promises," Ensign, May 1996, 17.

"I wish that every Latter-day Saint would remember these few words. How I wish that they were engraven upon our memories and upon our hearts, and that we would determine that God shall be bound to fulfill His promises unto us, because we will keep His commandments. There is a law irrevocably decreed in heaven--so we are told by the Prophet Joseph--before the foundations of the world, upon which all blessings are predicated, and when we receive any blessing, it is by obedience to the law upon which it is predicated [see D&C 130:20-21]. If you and I desire the blessings of life, of health, of vigor of body and mind; if we desire the destroying angel to pass us by, as he did in the days of the children of Israel, we must obey the Word of Wisdom; then God is bound, and the blessing shall come to us."  -Heber J. Grant, in Teachings of Presidents of the Church: Heber J. Grant [2002], 191-92
 

"Young people, stay in condition to respond to inspiration. I have come to know also that a fundamental purpose of the Word of Wisdom has to do with revelation. From the time you are very little we teach you to avoid tea, coffee, liquor, tobacco, narcotics, and anything else that disturbs your health. And you know that we get very worried when we find one of you tampering with those things.  If those "under the influence" can hardly listen to plain talk, how can they respond to spiritual promptings that touch their most delicate feelings? As valuable as the Word of Wisdom is as a law of health, it may be much more valuable to you spiritually than it is physically. Even if you keep the Word of Wisdom, there are some things that can happen to you physically, but those things don't generally damage you spiritually. When you become a father or a mother, don't live so that your children go unled because of habits that leave you uninspired.  The Lord has a way of pouring pure intelligence into our minds to prompt us, to guide us, to teach us, to warn us. You can know the things you need to know instantly. Learn to receive inspiration."  -Boyd K. Packer