If we confess (εαν ομολογωμεν). Third-class condition again with εαν and present active subjunctive of ομολογεω, "if we keep on confessing." Confession of sin to God and to one another (James 5:16) is urged throughout the N.T. from John the Baptist (Mark 1:5) on.

Faithful (πιστος). Jesus made confession of sin necessary to forgiveness. It is God's promise and he is "righteous" (δικαιος).

To forgive (ινα αφη). Sub-final clause with ινα and second aorist active subjunctive of αφιημ.

And to cleanse (κα αγιαση). So again with ινα and the first aorist active subjunctive of καθαριζω (verse 1. John 1:7).