Paul is not talking about salvation here. He was certain of his relationship with God… and he was talking to believers that were in that same relationship with God. He is talking about not allowing himself to get bogged down … and instead continuing to focus on the work that God set before him.
This is what you have been taught to believe, so that anti-Catholic theology can be maintained, but that is not what the scripture says.
Yes, Paul was certain about his relationship with God. He was also certain about the fact that people can, and do, walk away from that relationship, and that we have this ability right up the the point of death. He knew that, as long as he is on this earth, he could fall from grace, be cut off, become like weeds, whose end is to be burned.
Look at the context. The verse just prior to this says:
Phil 3:10-11
10… that I may know him and the power of his resurrection, and may share his sufferings, becoming like him in his death, 11** that if possible I may attain the resurrection from the dead. **
…“What we have attained” … is right standing with God … he says hold onto that foundation (already attained) … and, with that in place, press toward the goal of accomplishing the work set before you by God before the foundation of the world.
Yes, of course. Catholics call this right standing with God a “state of grace” or being justified. You are right that walking in the deeds that He has planned for us is absolutely essential to maintaining that state of right standing with God. If we abandon those works he has prepared for us, and involve ourselves with sin, we will be separated from that right standing. You see, Catholics believe that the nature of sin has not changed. Sin has always separated mankind from God, and still has the potential to do so.
Code:
"The prize of the upward call" is the reward that Jesus promised ... for a job well done.
For Catholics, the prize is salvation. Yes, there are rewards for a job well done, but attaining heaven is winning the race.
Rom 6:22-23
22 But now that you have been set free from sin and have become slaves of God, **the return you get is sanctification and its end, eternal life. **23 For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord.
Throughout this life we are being sanctified, and the end of that sanctification is eternal life. But we don’t assume that we have “already attained” the end result. The Apostles taught that, so long as we are on this earth, we will work out our salvation with fear and trembling. This is our upward call, eternal life being the prize.
Col 3:23-25
23 Whatever your task, work heartily, as serving the Lord and not men, 24 knowing that from the Lord you will receive the inheritance as your reward; you are serving the Lord Christ.
He speaks here of a singular “inheritance” as the reward for the hearty work. What is that inheritance?
1 Peter 1:3-9
3 Blessed be the God and Father of our Lord Jesus Christ! By his great mercy we have been born anew to a living hope through the resurrection of Jesus Christ from the dead, 4 and to an
inheritance which is imperishable, undefiled, and unfading, kept in heaven for you, 5 who by God’s power are guarded through faith for a salvation ready to be revealed in the last time. 6 In this you rejoice, though now for a little while you may have to suffer various trials, 7 so that the genuineness of your faith, more precious than gold which though perishable is tested by fire, may redound to praise and glory and honor at the revelation of Jesus Christ. 8 Without having seen him you love him; though you do not now see him you believe in him and rejoice with unutterable and exalted joy. 9** As the outcome of your faith you obtain the salvation of your souls. **
The inheritance, the outcome of our faith, is the salvation of our souls. This salvation/inheritance is kept in heaven for us. There are some who become justified, then fail to persevere in faith, and never become united with their inheritance.
Paul knows that the outcome of his faith has not yet been attained, but is being kept in heaven for him. He is currently enduring trials, and must persevere in those trials to “win the race”. If he does not endure the trials, he will be disqualified from the race.