Paul moves into one of the longest personal passages in Philippians, and yet he still uses this personal information to exhort the Philippian believers.
You can see the beginning of these personal remarks in Philippians 2:19-20:
Paul loves the Philippian church. They were instrumental in supporting his ministry, and maintaining him while he was imprisoned. This church sent financial gifts, and even sent people to assist Paul, Epaphroditus, who delivered the financial gifts they sent (4:18).
As a result, he shares a lot of personal information with them, interspersed throughout the letter. Typically, he would wait until the end of the letter to do so, as he does in most of his other letters to churches. But here, there are several sections within the body of the letter that show his heart more fully.
First of all, Paul expects to send Timothy to the church in Philippi soon. Timothy was his son in the faith, and was a steady help to Paul throughout his life and ministry. Paul also commissioned Timothy to serve the church, and wrote two letter instructing him, 1 Timothy and 2 Timothy. Paul relies on Timothy heavily, especially now that he cannot visit the church in Philippi himself, at the moment. Yet he does expect to be released, as we can see in verse 24.
Timothy’s task for now is to gather information and news about the church in Philippi and bring it back to Paul. Paul was very likely concerned about how his instruction was taken by the church, and how the problems were being resolved. And, by sending Timothy, he had a competent person in place to help instruct the church in such areas.