Paul calls us to selfless unity (1:27-2:4) and shows the example of Christ (2:5), who gave Himself up in deference to the Father (2:6-8) and did not exalt Himself (but the Father did!) (2:9-11). Then, in 2:12, Paul signals a conclusion to this section with the words "so then." Here, he harkens back to the ideas of 1:27 and adds two commands: one serious and one practical.
Serious Command (2:12-13): "Work out your [own] salvation" is the first command. This, of course, is a command to saved people being addressed in these verses (1:27-2:11). These are saved people. This is important to keep in mind because "work[ing] out your own salvation" does not mean save yourselves. Salvation is a free gift from God and these believers already possessed it through faith. This is then a command—not to merit salvation but—to carry out the implications of this free gift of God. Well, what are those implications? Paul explains in verse 15: "to be blameless and innocent… above reproach." This in one word is holiness. Saved people are to be set apart from this "crooked and perverse generation," and we are to "appear as lights in the world" (1:15b). Saved people are called to live holy! Anyone who denies that salvation obligates believers to holiness is theologically deranged!
Paul also emphasizes the seriousness of this command. We do this "with fear and trembling." No casual and flippant attitude will do! This is also coupled with an attitude of humble submissiveness, namely, obedience. Paul then tops it off with an explanation in 2:13 that God is the One "who is at work in you." We pursue holiness because God is pursuing this in us. To fight against this is to fight against God who is actively producing in us the desire ("will") and the power ("work") unto holiness for His own good pleasure.
Practical Command (2:14-16a): Paul then gives a practical command about holiness as our mode of life. We are to "do all things [mode of life] without grumbling and disputing." The former refers to grievances and the latter quarreling, and we are to be rid of both! It is this holiness in everyday life that sets us apart from this corrupt world. Unlike the world, we imitate the selfless Christ and show ourselves "children of God above reproach." We are done with self-interest, selfish ambition and egotism. And this all comes about as we hold fast "the word of life," the life-giving Word, the gospel (1:27).
 Examples: 1) Consideration of his presence or absence. "Whether I come and see you or remain absent" (1:27) is now "not as in my presence only, but now … in my absence" (2:12). 2) Actions toward our faith. "Striving together for the faith of the gospel" (1:27) is now "holding fast the word of life" (2:16). 3) Christian conduct. "Conduct yourselves worthy of the gospel" (1:27) is now "work out your salvation" (2:12).
 "own" (as ESV and NKJV include it) better reflects the intensive pronoun he-au-tōn (ἑαυτῶν) in the Greek.
 It goes without saying that these are saved people. They are "saints" (1:1). They have a Lord and God as their Father (1:2). God has already begun in them a good work of salvation (1:6). Their citizenship is in heaven (3:20). They have assurance of glorification (3:21).
 As Eph. 2:8 says, "it [salvation] is the gift of God" (the gender of the Greek pronoun points to salvation, not grace or faith). Also, Rom. 6:23 says, "the free gift of God is eternal life." Interpretations that suggest that we must save ourselves ignore the pervasive doctrine of Scripture that salvation is a free gift of God to believers.
 Paul affirms that God's righteousness comes through faith in Christ (3:9) and that God's people have their names in the book of life (4:3).
 kat-er-ga-zo-mai (κατεργάζομαι) means to "carry out" or "do" (cf. Rom. 7:15-20; 1 Cor. 5:3; 2 Cor. 12:12).
 Sometimes we think that a free gift must imply zero responsibility, but even everyday life shows that certain gifts come with a serious responsibility. Consider a free gift of tuition, room and board from generous parents. What comes with this gift is the responsibility of diligent study (at least!). A free gift of a fully paid off house comes along with it the responsibility to keep up that house and pay its property taxes, etc. The free gift of salvation is of this type and it comes with serious responsibility.
 Example: "Free Grace Theology." Cf. Wayne Grudem, Free Grace Theology (Wheaton: Crossway, 2016).
 Paul says this is to be carried out "just as you have always obeyed… now much more in my absence."
 The Greek emphasizes the word "God" in this verse by placing in the forward position.
 NASB italicizes "His" because this is technically an article. But it is anaphoric and points to God, the subject. Also, "to will and to work" are what occur within the believer, otherwise, "work" becomes tautological.
 Given the context of selfless unity (1:27-2:11), these are interpersonal in nature, not God-directed.
 It is "an aroma of life" (2 Cor. 2:17), "leads to life" (Mt. 7:14), brings "life and immortality" (2 Tim. 1:10).