1 "To all the saints in Christ Jesus who are in Philippi, with the bishops and deacons."
Here we have Scriptural basis for the two offices of the NT church... bishops (pastors) and deacons.
6 "being confident of this very thing, that He who has begun a good work in you will complete it until the day of Christ Jesus."
Our salvation is a process. It begins with the new birth, and culminates when we die and go to Heaven, or Jesus returns (whichever comes first). Once God begins the work of salvation in a person, He will see to it the work gets completed. God always finishes what He starts. This is the security of the believer.
18 "in every way, whether in pretense or in truth, Christ is preached; and in this I rejoice..."
In this section, Paul makes the point that not everyone who preaches the Gospel does it for the right reasons. Nevertheless, as long as their message is truly the Gospel, we should rejoice it's being preached. The Gospel has the power to transcend the imperfections of the preacher. (thank goodness)
21 "For to me, to live is Christ, and to die is gain."
Paul is saying, "If they let me live, I get to serve Christ. If they kill me, I gain Heaven." A win-win!