Philippians 1:18 "Only that in every way, whether in pretense or in truth, Christ is proclaimed; and in this I rejoice. Yes, and I will rejoice"

Paul rejoices that Christ is proclaimed, even if the speaker has bad motives.  It's a reminder of what Paul wrote to the Corinthians when he said "For I determined to know nothing among you except Jesus Christ, and Him crucified."  It's a reminder that the power of God doesn't rest in the speaker, but in the Word and Spirit that works to change a sinners heart.

Philippians 2:17-18 "But even if I am being poured out as a drink offering upon the sacrifice and service of your faith, I rejoice and share my joy with you all. You too, I urge you, rejoice in the same way and share your joy with me."

Paul rejoices in suffering for the sake of the gospel.  Are we even prepared to suffer for the gospel?  If so, do we rejoice in suffering knowing that it's a suffering for the sake of Christ and His gospel?

Philippians 2:27-29 "For indeed he was sick to the point of death, but God had mercy on him, and not on him only but also on me, so that I would not have sorrow upon sorrow. Therefore I have sent him all the more eagerly so that when you see him again you may rejoice and I may be less concerned about you. Receive him then in the Lord with all joy, and hold men like him in high regard"

Epaphroditus was the one who was sick and recovered.  His return to Philippi was to be a point of rejoicing for the Philippians.  They are to rejoice in the Lord for his recovery and his efforts in furthering the gospel.  Notice how they are told to hold men like him in high regard.

Philippians 3:1 "Finally, my brethren, rejoice in the Lord"

It seems that Paul's exhortation to rejoice in the Lord is related to then end of chapter 2, rejoicing in the Lord for Epaphroditus.

Philippians 4:4 "Rejoice in the Lord always; again I will say, rejoice!"

Again it looks as if Paul is rejoicing in the Lord for His provision of companions who are united in defending and proclaiming the gospel (vs3).

Philippians 4:10 "But I rejoiced in the Lord greatly, that now at last you have revived your concern for me; indeed, you were concerned before, but you lacked opportunity."

Lastly, Paul rejoices in the Lord that the Philippians are providing for him.

Paul constantly rejoices in the Lord who is working in these people to further the gospel.  Are we rejoicing in the Lord for those who are defending the faith along side us?  Are we rejoicing in the Lord for those who are our spiritual leaders?