Isaiah 6:6-7 speaks concerning the purging of Isaiah.
After Isaiah realized that he was unclean, he was purged by one of the seraphim, signifying the holiness of God (v. 6a).
Isaiah was purged with an ember from the altar (vv. 6b-7a). This ember signifies the effectiveness of Christ's redemption accomplished on the cross.
This purging by the seraphim with an ember from the altar took away Isaiah's iniquity and purged his sin (v. 7b).
Had Isaiah not been washed by God before his experience in chapter six? Yes, Isaiah had been cleansed, but he realized that he was still unclean. This indicates that we all need to realize that we are a totality of uncleanness. No matter how many times we may be washed, we are still unclean. We all must come to know ourselves to this extent.
In our experience, whether we are clean or unclean depends on the feeling of our conscience; and the feeling of our conscience depends on our seeing the Lord. How much we see the Lord determines how much we will be cleansed. The more we see the Lord and are exposed, the more we are cleansed. When our conscience is cleansed and is void of offense, we are able to contact God. According to our enlightened conscience, we are clean, but according to the actual facts of our situation in the old creation, we are not clean. How could the old creation be clean? As long as we remain in the old creation, we can never be completely clean, for the old creation is unclean. We need the redemption of our body. Once our body is redeemed, we will get out of the old creation. At that time, we will be completely clean.