A basic and unchanging principle, persisting through the whole spectrum of Jewish thought, is the awareness that man has the freedom to choose between good and evil.
This is one of the fixed and secure elements in Scriptures and in the writings of the sages, even those who were influenced by Greek and Arab philosophy.
It is also found in the Kabbalah.
What is more, one can say that this essential recognition of free will is so fundamental to Jewish thinking that it has come to be a test of the authenticity of the Jewish approach.
Almost without exception, a philosophical or religious system of thought that does not accept the axiom of man's free will does not properly belong to the truly Jewish sphere—even if it is totally orthodox in every other respect.
Thus, in the case of the Dead Sea sect, the Pauline Christians, and others, the acceptance of a preordained fate was one of the fundamental issues that marked their separation from the community of Israel as a whole, and although the principle of free will does not appear in all the formal "lists" of the essentials of Judaism (and certainly not in Maimonides' "Thirteen Principles of Faith"), it is of crucial importance.
One of the great minds of the Chasidic movement, Rabbi Baruch of Kossov, asserted this idea in his book, Sod HaEmunah (The Secret of Faith), when he wrote that, essentially, man should accept the apparently contradictory aspects of the problem of free will and recognize the existence of choice, while at the same time believing that the Hand of the Creator guides him in making that choice.
If, however, a person cannot accept both Divine providence and free will, he had better opt for the latter.
This recognition is an important guideline to the way a man lives his life, forms his thinking habits, and functions in the world.
–Rabbi Adin Steinsaltz
From "Fate, Destiny, and Free Will," in The Strife of the Spirit by Rabbi Adin Steinsaltz