By mercy and truth - that is, God’s (Psa 85:10); He effects the atonement, or covering of sin; and the principles of true piety incline men to depart from evil; or, “mercy” and “truth” may be man’s, indicative of the gracious tempers which work instrumentally in procuring pardon.
purged - expiated (as in Lev 16:33; Isa 27:9, Hebrew).