Warning: a little graphic.
Scubula: a greek word often translated as "loss". For example, Paul said, "But whatever gain I had, I counted as loss for the sake of Christ" in Philippians 3:7.
More accurately, this word is translated rubbish.
Even more accurately, this word means the liquid flowing inside your intestines. Poop. Crap. I'll let you fill in the other synonyms from there. Paul is saying whatever he considered important before Christ, he now considers as crap. Literally. That's in the Bible, ladies and gentlemen.
Paul is saying this is true of his former life as a Pharisee. It was a life perceived to be holy, but any life apart from Christ is a sinful life. All lives prior to Christ are defined by sin. Even now as Christians, we fall prey to sin daily. Even though we know this, it's still easy to fall into a self-righteous mindset. "Well, sure, I yell at people in traffic, but I'm not the only one. And besides it could be worse. At least I don't drink and drive."
However, all sin is a remnant of that former life of scubula. All my sin is scubula. Get a picture of that in your head. You're covered in crap. You're nasty. You've been rolling in it. Picture Jean Veljean from Les Miserables when he is rescuing Marius.
Suddenly someone completely clean comes and takes that on Himself leaving you clean. All you have to do is be willing for Him to take it. Wow.
I am dirty. My sin coats me. However, Jesus is pure. He is holy. He is clean. Therefore, in Him I am clean. My faith He has counted as righteousness. Good Lord, how undeserving am I.