2:17 The prospect that Paul might receive a death sentence soon arose again in his thinking. He described his present life as the pouring out of a drink offering in Israel's worship (cf. 2 Tim. 4:6; Num. 15:1-10; Num. 28:4-7). After the priest offered a lamb, a ram, or a bull as a burnt offering, he poured wine beside the altar. This was the last act in the sacrificial ceremony all of which symbolized the dedication of the believer to God in worship. The pouring out of the wine pictured the gradual ebbing away of Paul's life that had been a living sacrifice to God since his conversion.
The phrase "sacrifice and service of (or coming from, NIV) your faith"is a figure of speech (hendiadys) meaning the sacrificial service arising from your faith.
Even if Paul would die, he could rejoice that he had made a contribution to the Philippians' sacrificial service to God. He viewed himself and them as priests offering sacrifices to God, namely themselves (cf. Heb. 13:15).
". . . his apostolic sufferings and the Philippians' sacrificial gifts to him because he is an apostle combine to form a perfectly complete sacrifice to God."87
2:18 The Philippians would not rejoice over the prospect of Paul's death, of course, but over the knowledge that they as Paul had offered themselves as acceptable sacrifices to God (Rom. 12:1). The apostle urged them not to sorrow over their own trials and his, but to rejoice as they worked out their own salvation adopting his attitude toward their situation in life. They could share their joy with Paul as they communicated with him and assured him of their joy in the Lord.
