Musar zu Tehillim 37:28

This is a very, very primary matter. Know that, in truth, this is the most difficult work in Chasidut due to its great subtlety and because the evil inclination has much entry into this area. Therefore, its danger is enormous. For the evil inclination may convince a person to distance many good things as if they were evil and draw him near to many sins as if they were great mitzvot.

But if he guards all three properly, namely, purity (temimut) of thought, examination, and trust - then he will walk securely in truth and no evil will befall him, as Chana said in her prophecy: "He will guard the feet of His pious ones" (Shmuel 2:9), and likewise David said: "He shall not forsake His pious ones; they will be guarded forever" (Tehilim 37:28).

That which will help greatly in acquiring Chasidut is great observation and much contemplation. For when a person contemplates much on G-d's great exaltedness, blessed be He, and His absolute perfection, and the immeasurably great distance between His greatness and our lowliness, he will be filled with fear and trembling before Him.