Then will I sprinkle clean {n} water upon you, and ye shall be clean: from all your filthiness, and from all your idols, will I cleanse you.

(n) That is, his spirit by which he reforms the heart and regenerates his. See Geneva Isa 44:3

Wesley's Notes

36:25 Sprinkle - This signifies both the blood of Christ sprinkled upon their conscience, to take away their guilt, as the water of purification was sprinkled, to take away their ceremonial uncleanness and the grace of the spirit sprinkled on the whole soul, to purify it from all corrupt inclinations and dispositions.

Jamieson-Fausset-Brown Bible Commentary

25. The external restoration must be preceded by an internal one. The change in their condition must not be superficial, but must be based on a radical renewal of the heart. Then the heathen, understanding from the regenerated lives of God's people how holy God is, would perceive Israel's past troubles to have been only the necessary vindications of His righteousness. Thus God's name would be "sanctified" before the heathen, and God's people be prepared for outward blessings.

sprinkle . water-phraseology taken from the law; namely, the water mixed with the ashes of a heifer sprinkled with a hyssop on the unclean (Nu 19:9-18); the thing signified being the cleansing blood of Christ sprinkled on the conscience and heart (Heb 9:13, 14; 10:22; compare Jer 33:8; Eph 5:26).

from all your idols-Literal idolatry has ceased among the Jews ever since the captivity; so far, the prophecy has been already fulfilled; but "cleansing from all their idols," for example, covetousness, prejudices against Jesus of Nazareth, is yet future.

Matthew Henry's Concise Commentary

36:25-38 Water is an emblem of the cleansing our polluted souls from sin. But no water can do more than take away the filth of the flesh. Water seems in general the sacramental sign of the sanctifying influences of the Holy Ghost; yet this is always connected with the atoning blood of Christ. When the latter is applied by faith to the conscience, to cleanse it from evil works, the former is always applied to the powers of the soul, to purify it from the pollution of sin. All that have an interest in the new covenant, have a new heart and a new spirit, in order to their walking in newness of life. God would give a heart of flesh, a soft and tender heart, complying with his holy will. Renewing grace works as great a change in the soul, as the turning a dead stone into living flesh. God will put his Spirit within, as a Teacher, Guide, and Sanctifier. The promise of God's grace to fit us for our duty, should quicken our constant care and endeavour to do our duty. These are promises to be pleaded by, and will be fulfilled to, all true believers in every age.