"If I am not for myself, who is for me? And if I am for myself, what am I?" (Pirkei Avot 1:14)

The Baal Shem Tov taught that the words: "If I am not..." mean: if I have negated my existence to G·d, then no foreign thoughts can distract me."

In prayer, one must be completely divorced from physicality...

In prayer, one must be completely divorced from physicality, and not feel one's existence in this world. This is the meaning of: "If I am not for myself, who is for me?" Meaning, when I come to the level that I neither know or feel "if I am for myself" - that is, to not know or feel if I am in this world or not - then I will certainly not be afraid of foreign thoughts. For which foreign thoughts can approach me when I am separated from this world? This is, "who is for me?" - meaning to say, which foreign thought can approach me?

However, "When I am for myself," that is, when I consider myself as a separate entity in this world, then the opposite is true - I am not considered anything. This is the meaning of "What am I?" That is: "In what way am I important, and in what way is my worship important to G·d? For foreign thoughts will distract me,1 and it is as though I am not in this world at all. For a person is created to serve G·d, which I can not due to these thoughts." This also explains what the Sages said: "If I am here, all are here."2 (Succah 53a)

[Tzava'at HaRivash, p. 7a, 12a; translation and commentary by Rabbi Dr. Eliezer Shore for //baalshemtov.com;
A fine annotated translation into English by Rabbi J. I. Schochet of Tzava'at HaRivash is available from KehotOnline.com—KOL]