מים וטהרה

And about the reason that water purifies everything impure, I would think on the side of the simple understanding that it is in order that a man see himself with the immersion as if he is created at that time, [just] like the whole world was water before man was upon it - as it is written (Genesis 1:2), "and the spirit of God floated upon the face of the waters." And through this comparison, he place upon his heart that [just] like he is renewed in his body, he also renew his actions for the good, fix his actions and be exacting in the way of God, blessed be He. And therefore the Sages said that the purification is not fit with water that is in a vessel, but rather only with living water - or collected [water], which is on the ground and, in any case, not in a vessel - in order to place in his heart the thought as if the world was entirely water, and [that] he is renewed with his emerging from them, as we said. But if the water was in a vessel - or even if it passed through a vessel - this matter that we said would not be set in the thought of the one immersing. As there is a limit to all that is in a vessel, which is the creation of the hands of man. And therefore when he immerses in a vessel, he will not think as if the whole world is water like at the beginning [of Creation], and that he is renewed at that time. 'And the one who accepts, will accept; and the one who refrains will refrain.'

It is obviously clear that the laws concerning defilements and purities are biblical decrees, and not things which the human mind can determine; they are classified as divine statutes. So too, immersion as a means of ridding oneself from defilement is included among the divine statutes. Defilement is not mud or filth to be removed with water, but is a matter of biblical decree; it depends on the heart's intent. Accordingly, the sages have declared: If a man immersed himself, but without a definite purpose in view, it is as though he had not immersed himself at all. Nevertheless, there is some ethical allusion to this: just as one who sets his mind on becoming clean becomes clean as soon as he has immersed himself, even though nothing new is produced in his physical being, so one who sets his mind on purifying himself from all the spiritual defilements, namely wrongful thoughts and evil traits, becomes clean as soon as he made up his mind to abstain from those notions, and brought his soul into the waters of reason. Indeed, Scripture declares: "I will pour clean water over you, and you shall be clean; from all your impurities and idolatries I will cleanse you" (Ezekiel 36:25).