While many versions of the Bible view verse 8, with its "faithful saying" formula, as beginning a new paragraph, it is important to see its relation to the preceding teaching. Here Paul attaches a strong motive for living the life described in verses 1-2, the possibility of which verses 3-7 subsequently demonstrate.
Rather than creating a division, the assertion this is a trustworthy statement, which refers back to at least verses 4-7 (so Knight 1979:95), bonds verse 8 to the preceding discussion. As in its other occurrences (1 Tim 1:15; 3:1; 4:9; 2 Tim 2:11), this formula calls the readers to a fresh acknowledgment of what has been their common confession. The reason for doing so in this case, as in the others, is to encourage the readers to live the life that the theological statement declares to be a possibility. Verse 8 is a succinct conclusion to the whole of the teaching on the Christian life given in Titus. In it Paul drives home three points that we must not miss.
First, the Christian life is a life of active performance. We must not mistake this emphasis as evidence that Christian morality or ethics boils down simply to doing the best that is humanly possible. This instruction is for those who have trusted in God, and therefore the role of the Spirit and faith is assumed (Rom 8:4-17; Gal 5:16). Yet at the same time we must not misconstrue Christianity as a gift from God that operates independently of the one who has received it. The truth is, the reality of the new life in the Spirit is discovered only by those who dare to be actors instead of audience. This comes through clearly in the purpose given for Titus's emphasis on these things (Christian living, vv. 1-2, and especially its theological basis, vv. 3-7): so that believers may be careful to devote themselves to doing what is good. Here concentration of the mind is combined with effort. A decision to perform is integral to the Christian life.
Second, as it is performed this life will have visible results. Paul describes this performance with the term "good deeds." This is Christian life viewed from its visible outworking (2:7; 2:14; 3:1; see notes on 1 Tim 2:10). The nearest practical application of the term is to be found in the Christlike lifestyle outlined back in 3:1 and ahead in 3:14. Performed in this way, the genuine Christian life contradicts the claims of the false teachers, who ultimately denied God with their lifestyle completely devoid of good deeds (1:16).
Third, the living out of this life will benefit everyone. Herein lies the motive. In this new sentence Paul brings this qualitatively new life (the second these things good deeds) to bear on the lives of others. It is because this life of faith is inherently and manifestly good (NIV excellent) that it is able to be of benefit to everyone. But of what benefit? For several reasons it is likely that Paul is speaking from a missionary concern for those outside the faith. First, the unambiguous reference to believers in the first half of verse 8 suggests that the reference to everyone at the end is primarily to unbelievers (the same contrast appears in 3:1-2). Then, as in 2:5, 7-8, 10-11 and 3:2, so also in this case: the importance of the visible attractiveness of the Christian life is that it might point others to belief in God. Paul's thought is that since God's love in Christ has transformed the lives of those who have believed (3:3-7), the manifestation of that love in their lives (3:1-2, 8) should have similar results in the lives of others. Mission is one of the primary reasons for the performance of the Christian life in the world.