Here is the simple answer to the question of how important Christian conduct is: very important! The Bible is replete with verses that link Christian conduct with how the world sees Christ. “In the same way, let your light shine before others, so that they may see your good works and give glory to your Father who is in heaven” (Matthew 5:16). “By their approval of this service, they will glorify God because of your submission that comes from your confession of the gospel of Christ, and the generosity of your contribution for them and for all others” (2 Corinthians 9:13). “Keep your conduct among the Gentiles honorable, so that when they speak against you as evildoers, they may see your good deeds and glorify God on the day of visitation” (1 Peter 2:12).
If we liken Christianity to a movie, our good works can be seen as the trailer. When unbelievers see the love Christians have for one another and the good works they perform, they may think all sorts of evil things about Christians, but they cannot fault their conduct, and this abounds to the glory of God. Even in our witnessing and defense of the faith, we should conduct ourselves with gentleness and respect (1 Peter 3:15), not in angry, boastful tones.
The truth of the matter is that the gospel is already an offense to the unbelieving world (1 Corinthians 1:18); Christians should not add to the offense. This sentiment is clearly seen in Peter’s first epistle. He exhorts his readers that, if they’re going to suffer at the hands of evil men, let it be because they’re Christians and not because they were acting sinfully (1 Peter 4:14-16).
Another good portion of Scripture where this point is laid out is in Paul’s letter to Titus. In the second chapter, Paul gives Titus instructions on how to teach his congregation. At three separate points in this chapter, he illustrates the point we’re discussing here. Paul urges Titus to teach young women “to be self-controlled, pure, working at home, kind, and submissive to their own husbands, that the word of God may not be reviled” (Titus 2:5). Likewise, he exhorts Titus “to be a model of good works, and in your teaching show integrity, dignity, and sound speech that cannot be condemned, so that an opponent may be put to shame, having nothing evil to say about us” (Titus 2:7-8). Finally, Paul tells Titus to admonish slaves “to be submissive to their own masters in everything; they are to be well-pleasing, not argumentative, not pilfering, but showing all good faith, so that in everything they may adorn the doctrine of God our Savior” (Titus 2:9-10). In all three cases, Paul makes the point that Christian conduct is important in not only shutting the mouths of evil men, but also in guarding the integrity of the Word of God.
Consider the alternative. If Christians conduct themselves no differently from the outside world, what good is that? If indeed the outside world is watching and they see no difference between themselves and Christians, what motivation (if any) will there be for them to forego their unbelieving lifestyle? The unbeliever is already inherently hostile to the things of God (1 Corinthians 2:14; Romans 8:7-8). If Christians conduct themselves as the unbelieving world does, then all we do is invite scorn and charges of hypocrisy.
To be sure, no unbeliever will be saved by the good works of the Christian; the gospel must be presented. Furthermore, we all know that even at our best, we are still prone to sin. Yet the gospel is much more likely to be received positively if it is presented by a person who is humble and gentle than a person who is rude and disrespectful. Our actions can either help or hinder the gospel.