The following is an excerpt from
The MacArthur New Testament Commentary on Philippians 1.
To live in a manner worthy of the gospel of Christ is to live a life consistent with God’s revealed Word. That includes living a life that corresponds to the divine truth Christians profess to believe, preach, teach, and defend. In other words, it means living with integrity in every facet of life. This mandate is expressed elsewhere in the New Testament as walking “in a manner worthy of the calling with which you have been called” (Eph. 4:1), “in a manner worthy of the Lord, to please Him in all respects, bearing fruit in every good work and increasing in the knowledge of God” (Col. 1:10), and “in a manner worthy of the God who calls you into His own kingdom and glory” (1 Thess. 2:12; cf. 4:1). It means “showing all good faith so that [believers] will adorn the doctrine of God [their] Savior in every respect” (Titus 2:10), demonstrating “holy conduct and godliness,” and being “diligent to be found by Him in peace, spotless and blameless” (2 Peter 3:11, 14).
The church’s greatest testimony before the world is spiritual integrity. When Christians live below the standards of biblical morality and reverence for their Lord, they compromise the full biblical truth concerning the character, plan, and will of God. By so doing, they seriously weaken the credibility of the gospel and lessen their impact on the world. God’s people have always been at enmity with the world, because the world is at enmity with God (Rom. 1:28; 5:10; Eph. 2:3; Col. 1:21). But the world can hardly be expected to embrace a faith whose proponents so little emulate its standards of holiness and fail to manifest the transforming power of Christ.
When the unsaved look at the church and do not see holiness, purity, and virtue, there appears to be no reason to believe the gospel it proclaims. When pastors commit gross sins and are later restored to positions of leadership in the church; when church members lie, steal, cheat, gossip, and quarrel; and when congregations seem to care little about such sin and hypocrisy in their midst, the world is understandably repulsed by their claims to love and serve God. And the name of Christ is sullied and dishonored.
The gospel is the good news of salvation through Jesus Christ. It is the truth that “Christ died for our sins according to the Scriptures, and that He was buried, and that He was raised on the third day according to the Scriptures” (1 Cor. 15:3–4). It is the message Paul describes as “the power of God for salvation to everyone who believes, to the Jew first and also to the Greek” (Rom. 1:16). The point here is that those who belong to Christ through saving faith in His gospel should demonstrate that power by their changed lives (cf. 2 Cor. 5:17).