I uncover unity in Philippians 2 (written by Paul) and John 15 (as John writes of Jesus' ministry). In Paul's letter to the Philippians, he urges them to "work out your salvation with fear and trembling," (2:12-13). "Work out" means to practice or bring that which has already been begun to completion. God has begun a good work in us and will be faithful to bring it to completion (Philippians 1:6). He is working through us...how are we to be working? Why are we to work after we accept the gift of salvation? Not because we have to but because we want to, because we are so grateful for Christ's sacrifice and do not want to do anything to offend such a merciful, gracious God. If someone gave you a house to live in and it wasn't quite finished (say trim work & some painting), would you decline the gift? I would be so thankful and live in it as the finishing touches were being fashioned. To decline the gift altogether or complain about it would seem offensive and ungrateful. How much greater a gift is salvation? God saved us (past tense) from the penalty of sin. God saves us (present tense) from the power of sin and God will save us (future tense) from the presence of sin when we enter heaven.
What work do we need to do? I think a bigger picture can be seen when we take a look at Jesus' teaching at the Last Passover meal with his disciples in John 15 when he says, "I am the vine, you are the branches." A branch cannot draw nourishment from any other source other than the vine. It would not work for me to draw strength from any other source but Jesus. Think of a vine trying to get nourishment from a can of Diet Coke. That's absurd and it's absurd to think that I could be sustained by anything or anyone BUT the Vine, the Bread of Life, Jesus. Therefore whatever "I" do, it isn't really me doing it, it's God doing it through me. The branch doesn't give food and water to the grapes...it flows through the branch from the vine. So the good things "I" do, it's Jesus doing it through my body. If I detach myself from the Vine, I can do NOTHING! (John 15:5) Romans 11:18 also says "Remember it is not you who support the root, but the root that supports you." Jesus supports me.
So yes, I'm working out my salvation...working at abiding so the Christ can work through me to produce good fruit: love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control to name a few (Galatians 5:22-23). It is indeed a two-way flow. If I cut myself off by not abiding, He's still working, but the nourishment and strength He provides won't have any fruit to go to. And the vine is solid, even though I the branch can wilt in the stresses and trials of life. But the Vine, he's not going anywhere!
And while I'm working to remain connected to the Vine, I am to be humble, realizing that it is God who is working in me because He chooses me and because it gives Him pleasure to work in me (Philippians 2:13). The word "work" appears twice in verse 13 and means active energy, effective power or efficacy. This is how God works in me and makes me desire what He wants and enables me to do what He wants me to do. God always supplies the energy and desire to do His will.
My work is abiding, remaining with Him, to be united with Him, one with Him in heart, mind and will. The rest is God's work.