In these verses, Paul gives us 3 biographical illustrations of what it means to have the attitude of Christ, in His submission to God and thinking of others and serving them by putting them first.
(1) Paul, himself, who was willing to lay down his life in martyrdom as a drink offering, to deepen their faith by his example (v17-18).
(2) Timothy, who was most like Paul in sincerely caring for the Philippians, rather than seeking his own advancement (v19-24).
(3) Epaphroditus, who risked his own life for the work of Christ, in order to fulfil His God-given mission to bring aid to Paul in prison (v25-30).
Oxford Bible Church - Living in the Last Days (audio)