The thoughts must be trained. Gird up the loins of the mind that it shall work in the right direction, and after the order of well-formed plans; then every step is one in advance, and no effort or time is lost in following vague ideas and random plans. We must consider the aim and object of life, and ever keep worthy purposes in view. Every day the thoughts should be trained and kept to the point as the compass to the pole. Everyone should have his aims and purposes, and then make every thought and action of that character to accomplish that which he purposes. The thoughts must be controlled. There must be a fixedness of purpose to carry out that which you shall undertake. . . .
No one but yourself can control your thoughts. In the struggle to reach the highest standard, success or failure will depend much upon the character, and the manner in which the thoughts are disciplined. If the thoughts are well girded, as God directs they shall be each day, they will be upon those subjects that will help us to greater devotion. If the thoughts are right, then as a result the words will be right; the actions will be of that character to bring gladness and comfort and rest to souls. . . .
Those who move without thoughtful consideration, move unwisely. They make fitful efforts, strike out here and there, catch at this and that, but it amounts to nothing. They resemble the vine; its tendrils untrained and left to straggle out in every direction will fasten upon any rubbish within their reach; but before the vine can be of any use these tendrils must be broken off from the things they have grasped, and trained to entwine about those things which will make them graceful and well formed. . . .
By the ever-learning student new light, new ideas, new gems of truth will be found, and eagerly grasped. He thinks; the laws of the mind require him to think. The human intellect gains expansion and vigor and acuteness by being taxed. The mind must work or it will dwindle. It will starve unless it has fresh subjects to think upon. Unless it is made to think hard it will surely lose its power of thinking.--Letter 33, Feb. 27, 1886, to a minister working in Europe. TDG 66
We cannot obtain wisdom without earnest attention and prayerful study. Some portions of Scripture are indeed too plain to be misunderstood, but there are others whose meaning does not lie on the surface to be seen at a glance. Scripture must be compared with scripture. There must be careful research and prayerful reflection. And such study will be richly repaid. SC 90
Wherefore gird up the loins of your mind, be sober, and hope to the end for the grace that is to be brought unto you at the revelation of Jesus Christ; 1 Peter 1:13 (King James Version)