There were two rocks mentioned. Petra and Petros. The Rock spoken of for the Church is the large one which is Christ, not the small petros. Thats how I read the verse and my friends agree. It is good to pray for others, not to pray for those who are already dead. Praying for them will do nothing. They await resurrection and judgment at judgment seat before the 1000 years or at Great White Throne after the 1000 years.
The kingdom is in the future that is being spoken of. The kingdom has 3 aspects: todays outward conduct, the reign in the 1000 years and todays outward appearances. Since this verse is talking about entering the kingdom it is talking about the second usage of the 1000 year reign. Most Bible versions say iniquity, not as harsh as evildoers. Now since these are Christians and you can be born-again only once, then it is a loss of rewards of reigning in the 1000 years. Christians are capable of iniquity.