Q. Don’t Catholics have to earn their salvation?
A. No. We cannot earn salvation for we have been saved by grace. However, as always in all of God’s covenants with men: God does His part and we do our part.
+God gave Adam and Eve a garden; Adam and Eve were supposed to not eat from one tree
+God warned Noah to build an ark and fill it with animals so they would survive a flood; Noah built an ark and gathered the animals God saved them all.
+God promised Abraham to make his descendants as the stars of the sky; Abraham had to leave his home go to where God showed him
+God told Moses He would bring the Israelites back to the Promised land; the Israelites had to leave Egypt and conquer the Canaanites
+God sent His son to pay the eternal consequences of sin by death on the cross; we must pay the temporal consequences of sin through our sufferings in this life or the next.
Catechism of the Catholic Church
The Punishments of Sin
1472 To understand this doctrine and practice of the Church, it is necessary to understand that sin has a double consequence. Grave sin deprives us of communion with God and therefore makes us incapable of eternal life, the privation of which is called the “eternal punishment” of sin. On the other hand every sin, even venial, entails an unhealthy attachment to creatures, which must be purified either here on earth, or after death in the state called Purgatory. This purification frees one from what is called the “temporal punishment” of sin. These two punishments (eternal & temporal) must not be conceived of as a kind of vengeance inflicted by God from without, but as following from the very nature of sin. A conversion which proceeds from a fervent charity can attain the complete purification of the sinner in such a way that no punishment would remain.
II Sam. 12:13 Then David said to Nathan, ” I have sinned against the LORD ” And Nathan said to David, “The LORD also has taken away your sin; you shall not die. 14″However, because by this deed you have given occasion to the enemies of the LORD to blaspheme, the child also that is born to you shall surely die.”
Here we see God forgives David for the eternal consequences of his sin of sleeping with Bathsheba and having Uriah her husband killed; when David confesses and repents. But punishment for the temporal consequences of sin remains and his child from the adulterous union will die along with many other punishments and sorrows pronounced by Nathan in:
II Sam 12:10-12‘Now therefore, the sword shall never depart from your house, because you have despised Me and have taken the wife of Uriah the Hittite to be your wife.'”Thus says the LORD, ‘Behold, I will raise up evil against you from your own household; I will even take your wives before your eyes and give them to your companion, and he will lie with your wives in broad daylight. Indeed you did it secretly, but I will do this thing before all Israel, and under the sun.'”
In the New Testament verse below we see the doctrine of the necessity of purification from the temporal punishment for sin peeking out of St. Paul’s letter to the Colossians:
Colossians 1:24 Now I rejoice in what was suffered for you, and I fill up in my flesh what is still lacking in regard to Christ’s afflictions, for the sake of his body, which is the church.
CCC 1473 The forgiveness of sin and restoration of communion with God entail the remission of the eternal punishment of sin, but temporal punishment of sin remains. While patiently bearing sufferings and trials of all kinds and, when the day comes, serenely facing death, the Christian must strive to accept this temporal punishment of sin as a grace. He should strive by works of mercy and charity, as well as by prayer and the various practices of penance, to put off completely the “old man” and to put on the “new man.” http://www.scborromeo.org/ccc.htm