I think we need to take into consideration what the articles were referring to at the time they were written. No one who bears the name Anglican should accept the Roman Catholic doctrine of purgatory. No one should be teaching purgatory in the Churches, but to say that we cannot have a pious opinion about something is going farther than I am willing too. Jesus took our sins upon Himself. His victory is my victory by faith. There is no need to undergo purgatory. However, we still desire to sin. We are right in the eyes of God because of Jesus but we still want to do what is wrong. Do you think its against the formularies to believe we will be changed in the sense that we will not desire sin when we enter heaven? Just my opinion! I think this is all that Lewis was saying.