There are three things primarily: purgatory, praying for the dead, and the treasury of merit.
The treasury of merit is particularly interesting. It contains the merit of Jesus and the other saints who have a surplus. In particular, monks who separated themselves from the work and spent their time praying and doing other 'holy' things, were able to earn heaven and build up a surplus of merit that would help others who didn't have enough merit to earn heaven. Or something like that...
Quite contrary to the example Jesus left us on how to live.
Plus a very solid smackdown of the interpretation of predestination Calvin spewed :
Sirach 15:12 Say not : He hath caused me to err : for He hath no need of wicked men.
Sirach 15:13 The Lord hateth all abomination of error, and they that fear Him shall not love it.
Sirach 15:14 God made man from the beginning, and left him in the hand of his own counsel.
Sirach 15:15 He added His commandments and precepts.
Sirach 15:16 If thou wilt keep the commandments and perform acceptable fidelity for ever, they shall preserve thee.
Sirach 15:17 He hath set water and fire before thee : stretch forth thy hand to which thou wilt.
Sirach 15:18 Before man is life and death, good and evil, that which he shall choose shall be given him :
Sirach 15:19 For the wisdom of God is great, and He is strong in power, seeing all men without ceasing.
Sirach 15:20 The eyes of the Lord are towards them that fear Him, and he knoweth all the work of man.
Sirach 15:21 He hath commanded no man to do wickedly, and He hath given no man license to sin :
Sirach 15:22 For He desireth not a multitude of faithless and unprofitable children.