There is a common cultic heresy to the effect that the blood of Christ has no cleansing efficacy of itself, even though this contradicts the plain statement of our text. John wrote the above words long after Christ’s blood had all been spilled on the cross, but it was still miraculously cleansing sinners in His day, and is in ours as well.
It is true that Christ’s blood supported His physical life, for "the life of the flesh is in the blood" (Leviticus 17:11). But His blood was not like the blood of other men, for it was "the precious blood of Christ, as of a lamb without blemish and without spot" (1 Peter 1:19), uncontaminated either by genetic defects due to accumulated generations of mutations (as in all other men and women), or inherent sin.
When His blood was shed, it did not simply disappear into the ground and decay into dust, any more than did His body in the tomb, for it had been an integral part of His perfect human body which was to be raised and glorified. As our great High Priest, He somehow took the atoning blood into the holy place in the heavenly tabernacle. Into the earthly tabernacle "went the high priest alone once every year, not without blood, which he offered for himself, and for the errors of the people. . . . by his own blood he |Christ| entered in once into the holy place, having obtained eternal redemption for us" (Hebrews 9:7, 12).
There in heaven, at the mercy seat, just as the ancient high priest "sprinkled with blood" both the book and the people, the tabernacle and its vessels, so have we been cleansed in God’s sight by His own "blood of sprinkling" (Hebrews 9:19-21; 12:24; see also 1 Peter 1:2). Thus, His blood can (literally) "keep on cleansing us from all sin." HMM