You’re alluding to the Phil. 2:12 passage where Paul encourages the church at Philippi to
katergazomai, carry through, “keep on working out” (continuous present tense) the deliverance (salvation) of the church into a state of Christian maturity, with fear and trembling.
“
Fear and trembling” is an idiomatic expression for a
humble frame of mind:1 Cor 2:2-5 “For I determined to know nothing among you except Jesus Christ, and Him crucified. I was with you in weakness and
in fear and in much trembling, and my message and my preaching were not in persuasive words of wisdom, but in demonstration of the Spirit and of power,
so that your faith would not rest on the wisdom of men, but on the power of God.”
2 Cor 7:15 “His affection abounds all the more toward you, as he remembers the obedience of you all, how you received him
with fear and trembling.”
Eph 6:5 "Slaves, be obedient to those who are your masters according to the flesh,
with fear and trembling, in the sincerity of your heart, as to Christ;"This is seen quite vividly in context since Paul previously directs his readers to Christ Himself as the epitome of humility in Phil. 2:2-8."Therefore if there is any encouragement in Christ, if there is any consolation of love, if there is any fellowship of the Spirit, if any affection and compassion, make my joy complete by being of the same mind, maintaining the same love, united in spirit, intent on one purpose.
Do nothing from selfishness or empty conceit, but with humility of mind regard one another as more important than yourselves; do not {merely} look out for your own personal interests, but also for the interests of others. Have this attitude in yourselves which was also in Christ Jesus, who, although He existed in the form of God, did not regard equality with God a thing to be grasped, but emptied Himself, taking the form of a bond-servant, {and} being made in the likeness of men. Being found in appearance as a man,
He humbled Himself by becoming obedient to the point of death, even death on a cross.Unlike the first Adam, who made a frantic attempt to seize equality with God (Gen. 3:5), the Son emptied Himself by becoming a Servant and humbly accepted that role all the way to death by crucifixion, His death as our Substitute for the forgiveness of sins.
Paul, in context, was exhorting the church at Philippi to continue in that same
humble frame of mind to Christian maturity. The putting aside of all personal rights and interest, like Christ, in order to insure the welfare of others.
The idiomatic expression “
fear and trembling” has nothing to do with living out one’s life with the fear of losing salvation.
Paul goes on to say that in his own life whatever gains he had he now counts as loss, useless, even a hindrance, because they had to be unlearned for the sake of walking by faith

hil. 3:9 "…and may be found in Him, not having a righteousness of my own derived from (
the principle of) law,
but that which is through faith in Christ, the righteousness which {comes} from God on the basis of faith,"The contrast Paul presents here is
works-righteousness (based on the principle of law) vs.
faith-righteousness (based on the principle of grace), which, the latter is given (freely) by God. It’s Paul’s most concise statement of justification by faith alone.
Phil. 3:12: "
Not that I have already attained it (see vs. 10),
or have already become perfect (full knowledge and perfect conformity),“does not refer to his hope of attaining salvation (a gross misinterpretation), but to his
practical experience of knowing Christ (His death and the power of His resurrection, vs. 10). A reference to his
experiential/practical sanctification in this present life, not his salvation. He says, “…but I press on so that I may lay hold of (subjective)
that for which also I was laid hold of by Christ Jesus” (objective).IOW, Paul, in this life, continuously presses forward in his
experiential sanctification in view of that which is already his in Christ. A perfection which cannot be attained in our present, unredeemed, unglorified bodies (obviously some in Philippi were teaching they could, as do some today - “
supersaints” and
theosis”). But concerning this body he says

hil 3:20-21 "
For our citizenship is in heaven, from which also we eagerly wait for a Savior, the Lord Jesus Christ;
who will transform the body of our humble state into conformity with the body of His glory, by the exertion of the power that He has even to subject all things to Himself."Only then will “
perfection” be experientially realized - and that too by the power and grace of God toward us in Christ Jesus.