τὸ αἷμα Ἰησοῦ τοῦ υἱοῦ αὐτοῦ καθαρίζει ἡμᾶς ἀπὸ πάσης ἁμαρτίας. (1 John 1:7 WH)
S.M. Baugh asks whether this construction means "cleanses us from all sin" or "from every sin."
"'the death of Jesus his Son makes us clean from every sin' (or 'from all our guilt') 1 Jn 1:7" (Louw-Nida 88.310).
The OT formula is καθαρίσαι ὑμᾶς ἀπὸ πασῶν τῶν ἁμαρτιῶν ὑμῶν ἔναντι Κυρίου, καὶ καθαρισθήσεσθε. (See Lev 16:30; compare Ps 18:14; 50:4).
BDAG indicates that the expression ἁμαρτίαν . . . ἔχομεν (1 Jn 1:8) refers to "a state of being sinful, sinfulness."
Conversely, in 1 John 1:9, τὰς ἁμαρτίας ἡμῶν evidently pertains to "unrighteousness" (i.e., deviating from righteous human or divine standards).