Musar do Wyjścia 30:32

And our sages of blessed memory said of Moshe and Aharon regarding the "anointment oil" with which Moshe anointed Aharon, that they feared perhaps they would transgress somehow by using it unlike its commandment, for it was stated "It shall not be poured upon the flesh of a man" (Shemot 30:32). Thus our sages said (Horayot 12a):

Thus, we see that just like much contemplation is the way to acquire constant fear, so too interruption of thought and idleness of study is its greatest detriment, whether this is due to preoccupations or will - every interruption of thought is a nullification of the constant fear.