If a believer sins, are they still forgiven and cleansed?
Yes. The assurance is that even when believers sin, they remain under the blood, just as Israel in Egypt was protected by the blood, so nothing could touch them. They are still forgiven and still cleansed, though this grace is not licensed; believers must still have that cleansing.
Les explains that this is a glorious assurance: even when believers sin, they are under the blood, just like Israel in Egypt, where the death angel could not touch them. Believers must find themselves there. But Les stresses that this is not licensed; God's grace is not licensed. The promise is that if we sin, we are still forgiven and still cleansed, but we now have to have that cleansing. Les points to 1 John 2:2, where Christ is our advocate and propitiation, connecting it to the tabernacle imagery—the Holy of Holies, Ark of the Covenant, veil, showbread, candlestick, altar of incense, brazen laver, brazen altar, and sacrificial lamb—which he had explained earlier.