When are where does regeneration (being born anew, being made alive) occur? When we are placed into Christ, thus "together" with Christ we are made alive. Ephesians 2:5.When you say ///, where they undergo the washing of regeneration which removes their sin burden, what God held against them. /// Which verses say that regeneration removes the 'sin burden '? And how do we tie in 2 cor 5.19 which says ' not imputing their trespasses against them '
Colossians 2:11
and in Him you were also circumcised with a circumcision made without hands, in the removal of the body of the flesh by the circumcision of Christ;
Thus both the washing of regeneration and the circumcision of Christ occur after God places us "in Him." Now there are differing views as to exactly what is the "body of the flesh" but my view is it refers to our sin burden, what God held against us. Thus in Christ our sin burden is removed. See Romans 6:5-7.
2 Corinthians 5:19 says God is "reconciling" not reconciled the world (humankind) to Himself. Thus when every individual (a member of the world) is placed into Christ, God is reconciling the world to Himself. And yes, once we have been placed into Christ, we have been, past tense, reconciled. But the reason we have the message of reconciliation is to help in bringing the lost to Christ to be reconciled. Only those placed in Christ have their sin burden removed, such that God no longer is "counting their trespasses against them."