The apostle Paul wrote, “Therefore, my dear friends, as you have always obeyed – not only in my presence, but now much more in my absence – continue to work out your salvation with fear and trembling, for it is God who works in you to will and to act according to His purpose.” Philippians 2: 12, 13.
First, it’s important to note that the Bible mentions three phases of salvation. (1) Saved. This is the past; the moment of conversion when the believer is justified, declared innocent of all sin ( John 10: 9; Acts 16: 31; Romans 10: 9; Ephesians 2: 8, 9). (2) Shall be saved. This is the future; the moment when Jesus returns and the believer is glorified (Matthew 10: 22; Revelation 2: 7; 3: 21; 21: 7). (3) Being Saved. This is the present in which the believer is being sanctified against the power of sin (1 Corinthians 1: 18; 2 Corinthians 2: 15).
I believe Paul’s reference to working out salvation is in the context of “being saved.” During the process of God saving us via sanctification, Paul is encouraging us to stick with it in order that our salvation may be brought to its fruition or end.
Paul points out too that sanctification’s effectiveness is related to being obedient to the Lord. He urges us to continue in that vein, being mindful of God’s willingness to generously and personally guide us from within. As such, there should be naturally for the believer, a healthy fear and trembling due to not wanting to disrespect or offend the Lord in His mercy and compassion for us. That kind of reverence is what will keep us in partnership with God.