Paul also says 1st Corinthians 3:15 (KJV):
Why would a believer suffer loss, given that they are perfect in Christ? I agree that we are perfect in Christ, and I believe in purgatory. Scripture supports both, to my eyes.
You have that skewed.
The loss referred to there is the loss of rewards; which is the issue of various ranks and privileges that are an aspect of one's service within the Kingdom of Heaven in Glory one day.
There is the Inheritance, or Eternal Life.
And that is settled.
And then there is the Reward of the Inheritance (of said Inheritance).
It is comprised of various ranks and priveleges within the various offices of service in God's Kingdom in Heaven itself.
The Judgment Seat of Christ will determine who will be rewarded with what rank and what privelege, and who will be rewarded with less, that is; who will suffer loss of what could have been a greater rank and or reward as a servant in the service of God, in His Kingdom, that could have been his and unto the Son's glory in our glory, but for one's chosen values, words, and conduct in the here and now.
Values, words, and conduct, here will impact that then.
Values, words and conduct becoming of a son of God will work an eternal weight of glory, or in Glory now, and unto that day in Glory when said weight of glory will be revealed so as by the fire of the Lord's rightly divided Word.
Values, words and conduct becoming the course of this world will result in loss of said rewards.
It is an ever fascinating study all on its own - this study of what Heaven and its Glory will be like.
Just a matter of catching a glimpse of it in the Scripture rightly divided, followed by determining to study out all that the Scripture says about it, not only in word, but also in similarity in function with the much more detailed description of the Kingdom of Heaven on Earth described in Scripture.
For the things not seen are understood by the things that are, so that one is without excuse as to why one is unaware of what's what in Scripture as to these things...that differ.
Admittedly, it is Advanced Mid-Acts.
Thus, one has to at least come to a place where one's Mid-Acts schematic is basically up and running, and then some.
But even Darby saw some of these things before he was "Dispensational" - so its not like these things are not in the Scripture for anyone willing seek them out, to begin to understand them.
What little Darby had understood about this very issue was exactly what caused him to begin to break away more and more from the traditions of men.
Nihilo, put away your Catechism.
Try the Bible alone, for a good two or three years...to begin with.
Nevertheless, Romans 5:8 towards you.
For that passage is not so much about the Cross as it is about what one's perspective towards life and others can now be, because of the Cross.
Thus, though I strongly disagree with various of your stated, nevertheless, Christ died for both our foul ups.
So the Grace of Romans 5 towards you in the hope that you come to that Grace for you that cost the Son His Life in your stead.
Put away your treadmill and get to committing to memory Gal. 3:1-3 and verse 5.
Then get to believing those passages.