Does 1 John 1: 7 “the blood of Jesus Christ his Son cleanses us from all sin”, mean that the blood must be applied again and again each time we sin so that we are kept clean?.
Under the law sacrificial blood was shed many times and there were many washings with water (Heb. 6: 2); under grace, we have the blood of Christ and the washing of the water of the Word (Eph. 5: 26). Both blood and water in the NT are said to cleanse, but they must not be confused. Water is employed in Scripture as a figure of the Word of God applied by the Holy Spirit (compare John 3: 5; 1 Pet. 1: 24). The cleansing with water is a moral, internal cleansing beginning with the Holy Spirit’s application of the Word causing new birth. Once clean (John 15: 3), I must be kept clean (John 13: 10), to preserve communion with the Father (1 John 1: 9). Thus the application of the water (the Word) by the Holy Spirit is repeated. But with the cleansing of the blood of Christ, there is nether application nor repetition, and it is the blood that we have in 1 John 1: 7.
The blood is the price of redemption (1 Pet. 1: 18, 19) and this was paid once in contrast to the blood–shedding of the OT. The OT sacrifices perfected (completed) nothing, hence the need for repetition every time sin occurred. This is the great thrust of the argument in Hebrews 9 and 10. They were repeated; His can never be repeated. They “can never … perfect those who approach” (10: 1); His “has perfected in perpetuity the sanctified” (10: 14). They were “unable to perfect as to conscience him that worshipped” (9: 9); His has once purged us so that we have “no longer any conscience of sins” (Heb. 10: 2; 9: 14). Notice that word “perpetuity” which means “without interruption”. My sins can never be imputed to me, they have gone from the eye of God, and my guilt is removed completely. That perfection (completeness) cannot be interrupted if I sin now because all my sins were future when the sacrifice was offered. This is not communion, which requires the water; but justification, which requires the blood (Rom. 5: 9). When was the blood shed?—when Christ died. Hence if it is a question of imputation and guilt, then it is the blood of Christ; if it is a question of the moral cleansing of the soul and of restoration of communion with the Father, then it is the washing of the water of the Word. But the blood is for expiation.
If 1 John 1: 7 were to be interpreted according to the question, then it should rather read “If we do not walk according to the light, then the blood of Jesus Christ cleanses us …” But it doesn’t say that! It is not a question of how I walk, (according to the light), but where I walk (“in the light”), that is in the light of divine revelation. Why is the present tense (“cleanses”) used then if repetition is not meant? Because the point here is not one of time at all. It is the intrinsic value of His blood that is in view. It is what it does; not when it does it, and for that the present tense must be used. If I say aspirin cures headaches, I am not thinking of when I had a particular headache; but I am thinking of the inherent ability of the medication to cure such. Hence like other statements in John’s epistle, it is abstract. It is the inherent quality in the blood of Christ to cleanse sin.