’m worried that if I become Catholic I will end up in mild despair thinking I won’t be saved.
When one feels discouraged, then we turn to God and ask Him to increase our Faith and Trust in Him, engage our wills despite these feelings and pick up our cross and carry on.
It is a temptation to despair and to not trust God and in His Power when we give into thoughts that we are not saved, and instead a temptation to ‘save ourselves’ by being certain.
I mean, if I commit just one mortal sin I’m done unless I do Penance but how can that bring peace?
We are ‘done’ unless we repent of this sin, make an act of perfect contrition and go to the sacrament of confession/penance. Doing penance for that sin is separate to the forgiveness of that sin. We’re only ‘done’ if we refuse to repent of any mortal sin committed.
I tend to be scrupulous and sensitive at times when it comes to sin.
Then you’re like a lot of Catholics. There are a lot who are scrupulous, but who also with God’s grace get up each day, and persevere in living a Catholic life to the best of their ability in co-operation with Gods’ grace, who regularly go to confession and Holy Communion.
Roman Catholics live one day of peace when one day you can be a child of God and the next day a child of Satan simply for the commission of one mortal sin.
Because we’ve
chosen to commit the mortal sin, but we know God has provided us the way for us to be reconciled to Him and His Church through the Sacrament of Confession, to recover the life of sanctifying grace within our souls.
Think of driving a car. Knowing that we could be involved in a fatal accident each time we get in and drive somewhere, we still do! We accept it may happen, we drive carefully and with due attention to avoid such an accident to the best of our ability, but we are not paralyzed with fear while driving.
So it is with living as a Catholic. We go about our days, doing our best to avoid willfully commiting a mortal sin, but know that if we do, then we go to the Sacraments God has provided. He knows our weaknesses and inclination to sin and has provided the remedy in His Sacraments.
Don’t we all sin? Don’t we all lust, have prideful thoughts, covet, etc?
Yes, we all do sin. But with the help of Gods’ grace we can strive to overcome all mortal sins, and even strive to reduce the frequency of venial sins too. We don’t or shouldn’t ever become complacent regarding sin in our lives and just accept sin. We continually strive to do better - all by co-operating with God’s grace He freely gives us.