Paul ends the section on holiness (2:12-16a) with a reference to a shared joy among God's people. This is the joy gospel ministers have as they serve God's church. And this is the joy the church has as they receive their loving service.
A Shared Joy (16b-18): Paul states in these verses that the church's holiness will be grounds for his exultation "in the day of Christ" (2:16b). Paul often spoke this way. His future joy was tied to the church's sanctification. This is the joy that motivated him to labor to present the church "as a pure virgin" and as "complete in Christ." And their sanctification would show that his labors were "not in vain." But, there is another dimension to this joy. He would rejoice even if he were martyred and be cut off from this work. This is because his martyrdom would also be for them. It is his unrelenting commitment to the gospel to the Gentiles (ergo, the Philippians) that would lead to his death. Thus, he would gladly lay down his life for this gospel, which is for them. And he calls them to rejoice with him in this. This is a shared joy.
A Likeminded Minister (19-24): Paul then turns his attention to two other men. He explains that these men will be visiting Philippi soon (and he himself also). Verses 19-24 focus on one of these men: Timothy. This man is much like Paul, "of kindred spirit" (2:20) and "genuinely concerned for [their] welfare" (2:20). Even though there are many who seek after "their own interests," not so Timothy. This man was different. He was deeply "concerned" for the interests of the church. What is striking about this trait is that seeking the church's interests is seen as seeking "those [interests] of Christ Jesus" (2:21). This is to say: loving Christ's church is to love Christ. And Timothy was definitely a church-lover, and they knew it (2:23)! Lastly, Paul points out Timothy's loyalty. Like a child working with his father, so he served with Paul for the gospel. And so, with great eagerness he made plans to send Timothy to minister to them. What a great joy the church has in those who minister to them out of love for them and out of love for Christ!
 NASB's "reason to glory" is the Greek noun kau-chē-ma (καύχημα) which means a joyful boast or glory. NKJV renders it simply as "rejoice." The word "exultation" best captures the sense here.
 For Paul, "the day of Christ" always points to the saints' presence with Him at their glorification. Cf. Phil. 1:6 ("perfect it [the good work] until the day of Christ Jesus") and 1:10 ("sincere and blameless until the day of Christ"). The timing of this is rapture (1 Cor. 15:52, "we will be changed"), but this could also be death (1:23).
 1 Thess. 2:19-20, "who is our hope or joy or crown of exultation? Is it not even you, in the presence of our Lord Jesus at His coming? For you are our glory and joy." "exultation" in 1 Thess. is the word kau-chē-sis (καύχησις) which is a cognate of kau-chē-ma (καύχημα), the word used in Philippians. Cf. also Romans 15:16.
 Paul speaks in this way in 2 Cor. 11:2 ("I betrothed you to one husband, so that to Christ I might present you [as] a pure virgin") and Col. 1:28 ("We proclaim Him, admonishing every man and teaching every man with all wisdom, so that we may present every man complete in Christ").
 "because" in NASB is the conjunction ho-ti (ὅτι). This is better rendered as "that" as per ESV, NET and NKJV. Paul is stating here that his exultation will demonstrate he did not run or labor in vain.
 This is the same labor he expected after his release (1:22, "to live on in the flesh… will mean fruitful labor").
 "have reason to glory" and "not in vain" of 2:16 are contrasted in Greek. Both are prepositional phrases that begin with the preposition eis (εἰς). Their holiness is " unto his exultation" and "not unto nothing."
 "But" (2:17) contrasts death (2:17) from ministry labors (2:16). This starts off another dimension of this joy.
 "poured out as a drink offering [spen-dō (σπένδω)]" points to his death. Cf. 2 Tim. 4:6, "I am already being poured out as a drink offering [the same word], and the time of my departure [i.e., death] has come." This is also reflected in the contrast between labor and death contemplated earlier in 1:22-23. There, the contrast is between "to live on in the flesh, this will mean fruitful labor for me" vs. "to depart and be with Christ."
 Paul saw his death as "being poured out as a drink offering upon the sacrifice and service of your faith" (2:17b). This was also true of this imprisonment: "the prisoner of Christ Jesus for the sake of you Gentiles" (Eph. 3:1). Paul was imprisoned for the sake of the Gentiles. He was ultimately imprisoned because he evangelized and fellowshipped with Gentiles (Acts 21:27-29). Were he to die now, it would be for them.
 2:24, "I trust in the Lord that I myself also will be coming shortly."
 That there are many who do this is seen in the statement, "they all seek after their own interests" (2:21). The language here recalls the command given earlier to "not look out for your own personal interests" (2:4).
 The verb is me-rim-na-ō (μεριμνάω) which even describes anxiety (Matt. 6:25-34). This is a deep concern.
 This interplay between love for Christ and love for His church is seen in the Lord's conversation with Peter where the Lord calls Peter to love Him by tending/shepherding His church (John 21:15-17). The Lord truly saw the church as His body and even described persecution of the church as "persecuting Me" (Acts 9:4).
 Paul will send him because of his loyalty to the gospel and his love for the church. Hence, the conjunction "Therefore" in 2:23. The word "him" in that verse is more than just a personal pronoun and it is emphatic. It's literally, "Such a person, therefore, I hope to send." Timothy was best suited for this ministry to the church.