Idolatry is anything that is considered to be a god, a separate power, an independent entity.
Idolatry begins when something is considered to stand on its own, without a Master.
At that moment, a crack has been opened, through which all the evil in the world can pour.
The ultimate defilement, the nadir of being, was embodied in Pharaoh, who declared, "The Nile is mine, and I have created myself.”
The statement that "the Nile is mine" constitutes the beginning of the defilement, when he claims total ownership over something.
And the continuation of his statement, "and I have created myself" is the ultimate contamination, since he says that there is nothing else besides him.
At its root, the kelipah does not deny God or war against Him.
It only declares, "I, too, am something.”
But that something grows until it becomes everything.
The nature of holiness, on the other hand, is self-nullification, a state that the divine spark within us enables us to attain.
The entire being of great men, such as the patriarchs, who were a chariot for the Shekhinah, and Moses, from whose throat the Shekhinah spoke, is actualized self-nullification.
But in any Jew, "even the most worthless of worthless men and the sinners of Israel,” who has no trace of such self-nullification, a divine spark exists.
And that spark is the potential to make oneself nothing, to accept death for the sake of God.
Yet paradoxically, this is a person's core of life.
–Rabbi Adin Steinsaltz
From Learning from the Tanya by Rabbi Adin Steinaltz