Vain Thoughts^{*1872, Testimonies for the Church 3:82-84.}

All your^{*Note: Portion of a testimony addressed to two young people.} acts, however secret you may think they have been, are open to your heavenly Father. Nothing is hidden, nothing covered. All your acts and the motives which prompt them are open to His sight. He has full knowledge of all your words and thoughts. It is your duty to control your thoughts. You will have to war against a vain imagination. You may think that there can be no sin in permitting your thoughts to run as they naturally would without restraint. But this is not so. You are responsible to God for the indulgence of vain thoughts; for from vain imaginations arises the committal of sins, the actual doing of those things upon which the mind has dwelt. Govern your thoughts, and it will then be much easier to govern your actions.1TT 300.1

Your thoughts need to be sanctified. Paul writes to the Corinthians: “Casting down imaginations, and every high thing that exalteth itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ.” 2 Corinthians 10:5. When you come into this position, the work of consecration will be better understood by you both. Your thoughts will be pure, chaste, and elevated; your actions pure and sinless. Your bodies will be preserved in sanctification and honor, that you may present them “a living sacrifice, holy, acceptable unto God, which is your reasonable service.” Romans 12:1. You are required to deny self in little as well as in greater things. You should make an entire surrender to God; you are not approved of Him in your present state. ...1TT 300.2

In order to answer life's great ends you must avoid the example of those who are seeking for their own pleasure and enjoyment, and who have not the fear of God before them. God has made provisions for you that are ample. He has provided that if you comply with the conditions laid down in His word, and separate from the world, you may receive strength from Him to repress every debasing influence and to develop that which is noble, good, and elevating. Christ will be in you “a well of water springing up into everlasting life.” John 4:14. The will, the intellect, and every emotion, when controlled by religion, have a transforming power.1TT 301.1