"For there is one God, and there is one mediator between God and men, the man Christ Jesus, who gave himself as a ransom for all, which is the testimony given at the proper time." (1 Timothy 2:5-6)
Keeping this short and simple. Jesus Christ is the one mediator between a holy God and a wretched mankind. The pope cannot remit sins, either in this life or the next. Relics cannot remit sins. Even our good works are "filthy rags". It is only Christ, who "... entered once for all into the holy places, not by means of the blood of goats and calves but by means of his own blood, thus securing an eternal redemption." (Hebrews 9:12) What else is needed? "Thanks be to God for his inexpressible gift!" (2 Corinthians 9:15).