In his book, A Body of Divinity, Thomas Watson gives six (6) reasons for the necessity of sanctification in the life of a Christian. They are as follows:
1. God has called us to it. Watson cites 2 Peter 1:3, which speaks not only of God giving us “all things that pertain to life and godliness” but also having called us to His own “glory and excellence” (or “virtue” – KJV). He also points us to 1 Thessalonians 4:7, which says, “For God has not called us for impurity, but in holiness.” If you are a believer in Jesus Christ, make no mistake about it – God has called you to a life of holiness and sanctification.
2. Without sanctification there is no evidencing our justification. As he writes, “Justification and sanctification go together” (p.244). See 1 Corinthians 6:11; Micah 7:18-19. They must be kept distinct, but never separate. Although Watson does not necessarily spell it out as such, the concern here seems to be one related to our assurance. Without sanctification, what evidence or proof do we have that we have been justified by Christ?
3. Without sanctification we have no title to the new covenant. Part of the new covenant is that God gives His redeemed people a new heart. Ezekiel 36:26-27 says,
“And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh. And I will put my Spirit within you, and cause you to walk in my statutes and be careful to obey my rules.”
So if we do not have a new heart within us by the Spirit of God and so do not walk in the statutes of God and carefully obey His rules or commandments, we are not yet members of the new covenant.
4. There is no going to heaven without sanctification. Here Watson twice quotes Hebrews 12:14 which states, “Without holiness no one will see the Lord” (NIV). This same thing is explicitly taught in the Westminster Confession of Faith in its chapter dealing with the doctrine of sanctification:
They, who are once effectually called, and regenerated, having a new heart, and a new spirit created in them, are further sanctified, really and personally, through the virtue of Christ’s death and resurrection, by His Word and Spirit dwelling in them: the dominion of the whole body of sin is destroyed,and the several lusts thereof are more and more weakened and mortified; and they more and more quickened and strengthened in all saving graces, to the practice of true holiness, without which no man shall see the Lord. (Westminster Confession of Faith 13.1)
Notice that the writers of the Confession also use the language of Hebrews 12:14. In other words, without sanctification no man shall see the Lord (or go to heaven).
5. Without sanctification all our holy things are defiled. He writes, “A foul stomach turns the best food into ill humours [i.e. indigestion or illness]; so an unsanctified heart pollutes prayers, alms, sacraments” (p.245). See also Isaiah 1:10-17; Matthew 7:21-23.
6. Without sanctification we can show no sign of our election. Here he points us to 2 Thessalonians 2:13, which says, “But we ought always to give thanks to God for you, brothers beloved by the Lord, because God chose you as the firstfruits to be saved, through sanctification by the Spirit and belief in the truth” (ESV, italics mine). Watson writes,”Election is the cause of our salvation, sanctification is our evidence. Sanctification is the ear-mark of Christ’s elect sheep” (p.245).
Let all of this be a comfort to every genuine believer in Jesus Christ, and an encouragement to grow in the grace of God in sanctification. May it also serve as a wake-up call of sorts to any who have up to this point contented themselves with a hollow profession of faith, but have never known the grace of God in truth.