Paul is not advising them to work for what they already possess, spiritual salvation.
So, your phrase "spiritual salvation" basically means or relates to "Justification"
I agree with you that Paul is commanding Christians in Phil2.
Again he is speaking about progressive sanctification, which saves (saved having a range of meanings determined by the context and first principles) us on the level of soul/mind.
I agree in concept, but Paul uses the word "salvation" and if I know and understand as you clearly seem to that salvation is a process and I can see that Paul is commanding Christians, then I see no reason to change Paul's language. In fact, I see problems created when we change the language of Scripture.
In addition, Paul is clearly commanding work to be done by the Christian in salvation. I've never said anything about keeping or loosing salvation here. Until we grasp that we do work together with God in our salvation, just as we are commanded to do here by Christ's Apostle and thus Christ, there really is no discussion I want to have re: keeping or loosing salvation.
Sanctification being distinct and separate from justification.
Again, this is a theological construct because when we are justified, we are also sanctified.
ESV 1 Corinthians 6:11 And such were some of you. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God.
ESV Heb. 10:10 And by that will we have been sanctified through the offering of the body of Jesus Christ once for all.
I simply believe the Text is inspired and I don't like men confusing my understanding
Why in "fear and trembling" because they may lose their justification, NO, that is not all what he is saying, in fear and trembling
is also seen here.
Again, I've made no statements re: keeping or loosing. I'm simply first arguing for some accuracy re: work because IMO this works salvation debate is a mess.
Also, I said the fear and trembling in 2:12 in context is related to 2:13 and speaks of the Christian not getting at cross-purposes with the Father who is working - providing capacity - for the Christian to do what he's being commanded to do. IOW our Father obviously wants us to be working with Him to accomplish our salvation and we best understand this.
“But the woman, fearing and trembling, knowing what had happened to her, came and fell down before Him and told Him the whole truth.” (Mark 5:33, NKJV)
That she fell down before Him tells me this "fear and trembling" is a positive response to God's working in our lives because this is not automatic as some like to teach (cough, cough) it is a process we need to learn about and put to work. (See James)
Fear and trembling is attached to a few very important words and concepts, one of them being godliness. It's something I think many of us comprehend as an edge we should maintain to whatever degree because we have a perfect Father and a perfect First-Born Brother and Lord whom our Father is raising us to be in the form of. IOW, when in this life do we not have a Father who can execute some discipline He deems necessary [to save us]?