I think Purgatory makes a lot of sense. It explains what happens to us when we die while retaining love and/or attachment to sin not leading to death.
There are two kinds of sin, sin that leads to death and sin that does not lead to death.
Each kind of sin has its own result, which means there are two kinds of results for sin. The sin that leads to death has everlasting suffering as its result. The sin that does not lead to death has temporary suffering as its result. The death of Christ remits the everlasting result (if we accept what He did according to His conditions), but not the temporary result.
When we die, there are two alternatives. I will call them Alternative 1 and Alternative 2. There can be no sin and no love of or attachment to any kind of sin in Alternative 1. If we die while retaining some love for and/or attachment to our sins that did not lead to death, we must relinquish that love and attachment before we can experience Alternative 1. Let’s call this relinquishment process The Accountability Machine. If we are in The Accountability Machine, it means that we have accepted Christ’s conditions for Alternative 1, but there is still a process we must undergo due to our love for and/or attachment to sins that did not lead to death. It is an unpleasant process because we love and are attached to those sins (the sins that don’t lead to death)–we struggle with giving them up. We are still saved—there is only one way out of The Accountability Machine, up (it’s a top loader, lol). Christ’s death and resurrection does not automatically mean we have relinquished our love and attachment to sin that doesn’t lead to death. We will be held accountable for it, but not in an everlasting way.
If we die but have not followed Christ’s conditions for Alternative 1, then we will experience Alternative 2.
I am not certain how Catholic this explanation is, but I think it works pretty well under a Catholic paradigm. Typically, Catholics talk about two kinds of punishment for sin. But punishment has a purpose. Suffering can be the result of temporal punishment (due to our love for and attachment to sins that don’t lead to death), but its purpose is to help us let go of that love and attachment. See, for example, Hebrews 12.
The question is: if we are otherwise saved, what happens to us when we die with our love and attachment to sin still intact?