Yes, the one sacrifice of Jesus on the Cross won us our salvation. In this we all agree. But notice that by this we are sanctified, i.e. made holy, not just justified. Is there any sinfulness, any selfishness, still lurking in your soul? If so, then this process of sanctification won by the price of the Cross is not yet complete.
Bookmark
And won't be completed in this life. As for faith alone, Ephesians 2:8-9. Where does Paul credit anything but faith, itself a gift?
“We are all sinners and fall short of the glory of God.” THAT’s why He has also given us grace. His death covers all our sins...ALL of them if we but ask.