As a recovering legalist, one of the “driving” motives behind the creation of this site was (and is) a desire to help other recovering legalists better understand how to pursue holiness in their daily lives (see The Reason for this Site).
The underlying, motivating truth for this daily pursuit is summarized by the subtitle of this site:
“growing in holiness by living in union with Christ.”
Union with Christ is the wellspring of all the believer’s spiritual blessings and subsequent experience of these blessings, which includes holiness (cf. Eph. 1:3-14; 1 Cor. 1:30). The whole of our Christian lives are to be centered on and motivated by our union with Christ.
“True holiness springs from union with Christ.”
The daily exercise of the believer in regards to the pursuit of holiness (i.e., sanctification) is to recall to mind his union with Christ.
As a believer grows increasingly aware of his union with Christ, he is motivated (i.e., gospel-driven) to pursue holiness and glorify God. Paul writes to the Corinthians,
15 Do you not know that your bodies are members of Christ? Shall I then take the members of Christ and make them members of a prostitute? Never! 16 Or do you not know that he who is joined to a prostitute becomes one body with her? For, as it is written, “The two will become one flesh.” 17 But he who is joined to the Lord becomes one spirit with him. 18 Flee from sexual immorality. Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body. 19 Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, 20 for you were bought with a price. So glorify God in your body, (1 Cor. 6:15-20, ESV emphasis mine).
Thus, apart from union with Christ, there is no possibility, power or proper provocation (i.e., motive) for pursuing holiness. There is only a “form of godliness, but denying its power,” (cf. 2 Tim. 3:5).
Thomas Boston writes,
“There are none that walk so exactly, but they are still making wrong steps, and contracting new defilement, which cannot be purged but by the application of the blood of sprinkling; nay, there is not one step the best make, but there is some defilement cleaves to them in it, so that still they need to wash their feet, John xiii. 10. This, then, is the daily exercise in the narrow way, and there is no walking in it but in Christ, as there is no true holiness but in communion with Christ…
True holiness springs from union with Christ; the Spirit applying the blood of Christ to the soul received by faith, improving the word, sacraments, and afflictions. The Spirit is the efficient, the blood of Christ the meritorious cause and faith the instrumental cause of true sanctification; but these others (i.e., common civility, morality, external duties of religion-J.F.) have a far lower rise. They are the effect of good education and breeding; of unsanctified consideration of their own circumstances and worldly interest, that oblige many to take up themselves, and live regularly; of fear and hope; of respect to credit and reputation, and in some legal convictions…True holiness is a cluster of the fruits of the Spirit…
…civility, morality, and a form of godliness, are acts of moral discipline, which have self-love in an unrenewed heart for their principle, the reason of them is not the will of God commanding them; they do not their works in faith of the promising assistance from heaven, nor of acceptance for Christ’s sake; but out of their own stock, little valuing whether they be accepted or not, or if they do, looking for acceptance on their intrinsic worth. Their end is not the glory of God, and to express their gratitude; but as they come from self, so they are swallowed up in self,” (Gospel Truth, pp. 234-235; emphasis mine).
From beginning, middle and end, the Christian life is a gospel-driven life (i.e., Christ-centered; lived out of one’s union with Christ). For, it is only in union with Christ that true gospel holiness is found and experienced.