Thoughts and Fantasies:

1. Make sure that you don't allow your mind to become chametz -- leavened. Don't dwell on bad thoughts or desires at all. These thoughts are rooted in the side of death. If they come into your mind, just reject them and push them out completely, because ultimately they ruin the mind and make it impossible to pray properly and experience genuine joy. You should try and avoid even the merest hint of thoughts like this. You should be as carful about it as we are to avoid even the merest speck of chametz on Pesach. Evil thoughts are the leaven in the dough, and the law regarding leaven on Pesach is that we must destroy it completely so that it can neither be seen nor found. Purify your mind and empty it of any thoughts like this (Likutey Moharan 5:4).
2. A person can't always stop bad thoughts from entering his mind in the first place. But he does have the power to reject them once he becomes conscious of them. This is something very important, because it is the way to make amends for sins he may have committed earlier in his life. Perfect repentance has to balance the original sins exactly, and this is literally what happens here. Before, when he sinned, it was because the temptation entered his mind and he succumbed to it. Now the thought is in his mind again, but this time he rejects it. So don't feel discouraged if you find all kinds of temptations and fantasies continually pressing in on your mind. They are actually providing you with the opportunity to repent and make amends for the damage done in the past. Today you have the power to master your thoughts and temptations. When you do so, the sparks of holiness which fell because of your earlier transgressions are released, and you are able to purify yourself. Your mind and your voice will be purified and you will find harmony and peace. This peace can bring the whole world back to the service of God (27:8).
3. When a person admits unholy thoughts to his mind, the holiness of his mind is reduced in direct proportion to the space occupied by these degraded thoughts. If you stick a pole in a river bed, all kinds of dirt and filth gather round it. In the same way, all kinds of bad characteristics develop because of these unholy ideas, and the mind is assailed with desires and temptations. In fact all the sins a person does are ultimately caused by the unholy ideas he originally admitted to his mind. To achieve true repentance, you must rid your mind of these thoughts. The mind is the soul, and when a person sanctifies his mind, he elevates and returns everything to its root. This is the essence of repentance (35:1).
4. Unholy thoughts are the `folly of the heart.' When a person dwells on such thoughts his heart becomes sullied and the `foreskin of the heart' grows thick. The `void' of the creation is spoiled, and it is as if this person had damaged the whole world. But when he thinks good thoughts, the creation is restored. When a person purifies his heart and expels all unholy thoughts from his mind, thinking only good thoughts, he can bring about real miracles (49:1).
5. A person's entire destiny for good or ill depends on the thoughts in his heart. The thoughts and ideas in the heart are the basis of the heart's `inclinations' -- the good inclination and the evil inclination. Good thoughts are the good inclination, bad thoughts are the evil inclination (Ibid.).
6. When a person expels all the unholy thoughts from his heart and thinks only good thoughts about ways of serving God, then he has founded his strength on the `rock of my heart' (Psalms 73:26) and he will succeed in reaching the level where `my heart is void within me' (Psalms 109:22). He will be able to develop his character to perfection and take on the yoke of heaven with a perfect heart. He will be worthy of true prayer and perfect repentance, and bring about unification in the worlds above and the worlds below. The hidden Torah of the Ancient One will be revealed, the forces of evil will be destroyed and the forces of holiness will be elevated. Israel will be blessed with vitality, abundance and prosperity (Ibid.).
7. All the thoughts which pass through the mind are always expressed in words. At the moment one thinks a thought, `the lips move' (cf. Yerushalmi Berachoth 7a). He may not actually feel this, but as the Zohar explains, there is always a movement, however subtle. Every thought that a person can think must be expressed in words, however subtly (66:4).
8. Many people experience very strong mental distractions while they are trying to pray. These can be immoral fantasies or even thoughts about idolatrous worship. There are even cases where people see vivid images of idolatrous objects or else they experience overwhelming temptations the very moment they stand up to pray. They try to push the thoughts out of their minds by tossing their heads from side to side. But the harder they try the more the thoughts press in. This is in the nature of thoughts like these. The more worked up you get about trying to push them out of your mind, the more they insinuate their way in. The best way to deal with them is simply to ignore them. Act as if you were completely unconcerned. Refuse to listen. Carry on with what you were doing, studying, praying, working or whatever. Pay no attention to the thoughts or fantasies at all. Don't keep on looking round to see if they have gone away. Just carry on with what you are trying to do. In the end they will go away of their own accord. But you should understand that this method is only a temporary measure. In the long term the task is to sanctify and purify your body. To achieve this you must go to the Tzaddikim to learn the paths of truth. Thoughts like these will then disappear completely (72).
9. If you allow yourself to be depressed about these kinds of thoughts it simply feeds them with more fuel. It is no good being upset or afraid of them. Just don't pay any attention to them. Try and be cheerful. Elsewhere we discuss the way to be happy always (see Simcha) Eventually these thoughts will disappear automatically. Don't keep on testing to see if they are still there. It won't help if you keep on turning round to look. Just don't pay any attention to them at all (Ibid.).
10. The Torah distinguishes between the animals which are pure and those which are impure. The `pure animals' are pure thoughts, and `impure animals' are impure thoughts. The battle between the different thoughts in a person's mind is a battle between the pure and the impure animals. Heaven allows them to carry on fighting because God has great pleasure when He sees a man struggling hard to defeat these `wild animals' (233).
11. The simple fact is that it is impossible for two thoughts to be in the mind at one and the same time. It is therefore an easy matter to rid yourself of bad thoughts by being quite passive. Simply don't think them. Think something else instead: think about Torah or devotion to God, or even about your work, and so on. If you just turn your mind to something else the bad thoughts and fantasies will go away automatically (Ibid.).
12. Thought is a very elevated level. One who wishes to think only thoughts of holiness and ascend to the world of thought must be completely silent. Even saying something good and noble would spoil the thought. But even when a person is completely silent, there are still many distractions which confuse the mind. He still has to purify his thoughts. The way to do this is through hearing and telling stories of the Tzaddikim (234).
13. Sexual fantasies are the prime source of all impurity. They are as strong a source of pollution as a dead body. Charity gives some protection against these fantasies, but one should never rely on this and permit oneself to talk freely with women. One should say only what is essential. The merit of the charity he gives will then save him from harm (242).
14. There are certain fantasies which derive their strength from a particular husk which is extraordinarily tough. It is very difficult to escape from them. Even if you try to shut your eyes the thought appears wherever you turn. Charity gives protection against these thoughts (Ibid.).
15. Whenever you find bad thoughts and fantasies pressing in on your mind, don't be depressed. Try extra hard to turn aside from them. The effort itself is very precious and brings about a great tikkun (Likutey Moharan II, 5:7).
16. A person's thoughts are in his power completely. He can turn them in whatever direction he wants. It may be that at times your thoughts run wild and fly to areas you ought to keep away from. It is still within your power to take them in hand, even against their will, and direct your thoughts to the true path. Thought is just like a horse which turns aside from the road and tries to go in the wrong direction. The rider controls the horse with the bridle and forces it to go in the right direction. As soon as you see your thoughts pulling in the wrong direction, take them in hand and bring them back to the right direction (Ibid. 50).
17. It is impossible to form any conception of the preciousness of good thoughts -- thoughts of Torah and devotion. Out of thoughts such as these there are formed perfect objects which will exist for all time. From this alone you can understand the true evil of unholy thoughts, God forbid (53).
18. You should aim for the level of Mah -- `What?' This means binding yourself and your thoughts to God at all times in order to draw Godliness over yourself. If you do this, all the battles and difficulties in your life will melt away and everything will go your way. The Hebrew word for `thought' is machshavah, which bears the meaning of `think what?' -- chashov-mah. That is to say, you must draw Mah? into your mind and bind your thoughts to God at all times. The gematria of Mah is: 45. This is equivalent to the gematria of the name of God when all the letters are written out in full.
19. You must be very careful about what you think: a thought can literally take on a life of its own (46).
20. Thought is man's highest aspect. It is more elevated than vision, the sense of hearing, and in fact everything. With thought it is possible to climb ever higher. This is why you must be so careful about what you think (Ibid.).
21. Sometimes a thought -- a good idea, or a glimmer of perception -- can pass through your mind and shine there for a moment and then fly away again. It takes great strength to run after the thought and chase it until you catch up with it (58).