
What does it take to see the Lord? Especially, what is essential to seeing him in the last day? What does it take to see him, not as the Judge condemning you, but as your Shepherd, as your Redeemer, welcoming you into his eternal presence?
Strive for holiness. Holiness is essential for seeing God. Were I to suggest that essential for seeing the Lord is holiness, the reaction might be, “that sounds like basing salvation on works.” The response to “ How good do I have to be to get into heaven?” is “better than you can be — 100% obedient. We very properly recoil from the suggestion that our works have any meritorious role in our salvation .That was something learned afresh at the time of the Protestant Reformation. And yet Hebrews 12:14 tells you: “Strive for peace with everyone, and for the holiness without which no one will see the Lord.” Sanctification is sometimes reduced to simply being fruit and evidence of justification. Scripture treats sanctification as something distinct from, something in addition to, and thus decidedly more than just fruit and evidence of justification. Parallel to repentance, sanctification is never the ground or basis for your justification, but it is something that is an essential part of belonging to Christ. The author of Hebrews is no less clear than Paul that our salvation rests on nothing that we do or are, but only on Christ himself: “He has no need, like those high priests, to offer sacrifices daily, first for his own sins and then for those of the people, since he did this once for all when he offered up himself” Heb. 7:27. The Holy Spirit, through Hebrews, is calling you to turn from self-righteousness and to trust in Christ alone for salvation.
“Sanctification has especial regard to God. Even though the whole world blazes with war, we must not let go of sanctification because it is the chain which binds us in union with God…. No one can see God without sanctification since we shall only see God with eyes that have been renewed according to his image.”
John Calvin, Commentary on Hebrews, at 12:14

Pursue holiness as you pursue peace. The harvest of righteousness and peace flows from the Lord’s discipline. Your discipline is evidence that you belong to the Lord’s family. Notice how Hebrews guards his language. You are responsible for making every effort to live at peace — you do not necessarily control the result. Some people resist peace. This is not peace at any price. Your first commitment is to the Lord. Thus you need to pursue holiness as you pursue peace.
Live as the family of God. In Leviticus 19, the reason you need to love your neighbor is that God is holy, and you are to reflect that holiness. A theme running through the Book of Hebrews is the idea of sonship, the fact that God’s people are children of God, brothers and sisters of Jesus Christ. The first chapter focuses on the unique person of the Son. He is greater than the angels. Chapter 2 describes his humiliation and exaltation — for the purpose of bringing many sons int glory. He came to “destroy him who holds the power of death — that is the devil — and free those who all their lives were held in slavery by their fear of death” (2:14–15). The center of the book focuses on the covenant. Jesus has brought us into fellowship with our holy Creator. Chapter 12 returns to the theme of children of God. He disciplines us, not out of vengeance, but precisely because we are his children. One of the reasons for holiness is this is the way that the family of God reflects their Creator/Redeemer. Paul and Peter emphasize that as God’s people our lives need to reflect the character of our Lord. The Heidelberg Catechism, Lord’s Day 32, gives as a motive for living a holy life, “and that by our godly walk of life we may win our neighbors for Christ.” In an increasingly chaotic culture, your life, the way your family conducts itself, can be a shining light pointing to your Savior.
See the Lord. The Lord is working in you. Certainly your sanctification, your holiness, is motivated by gratitude. Hebrews has just pointed you to the perfect Redeemer, Hebrews 12:2. But if you see justification as God’s work and sanctification simply as your inadequate response, you have missed the point that Hebrews is making. Yes, you are active in sanctification, you pursue holiness. But you do so because God is working in you. Lord’s Day 32, reflecting the language of Paul, speaks of Christ renewing us by his Spirit. Because holiness is essential to seeing the Lord, the Holy Spirit works in the Christian, shaping him to his glory. Neither works nor even faith are the basis of salvation — the basis is always the perfect obedience of Christ, imputed to the believer. Because holiness is essential to seeing the Lord, Hebrews summons you to strive for it, admonishing you to seek something that God is working in you. And thus both the Scriptures and the Confession can rejoice in the Spirit-wrought good works which are the fruit of sanctification. Perhaps we fail to delight as readily as we should when we see in the lives of God’s people the growth in holiness which flows out of union with Christ. We have a Scriptural imperative to stir one another (and ourselves) up to good works (Hebrews 10:24).
“In the matter of sanctification, it seems to me, we must confront a tendency—which is, unless my impression is wrong, pervasive, within churches of the Reformation — to view the gospel and salvation in its outcome almost exclusively in terms of justification…. The effect of this outlook, whether or not intended — and no doubt it is often the latter — is that sanctification tends to be seen as the response of the believer to salvation, defined in terms of justification…. With such a construction justification and sanctification are pulled apart; the former is what God does, the latter what we do, and do so inadequately.”
Richard B. Gaffin, Jr., By Faith, Not By Sight: Paul and the Order of Salvation, p. 86
See Jesus, the mediator of the new covenant. In the glorious scene of the assembly in the Jerusalem above, central is Jesus, the mediator of the new covenant. Hebrews has focused on Jesus throughout his book. Now he calls you to be united with him by faith. Where that faith is found, God not only justifies, he also sanctifies his people. All of your salvation is his work. To him be the glory. Where that kind of changed life takes place, people notice. When automatic anger is replace with self-control, not only is Christ honored, but your neighbors see something of his peace-making work in your life.
The believer’s future, perfect sanctification flows out of the Spirit-wrought process of growing in holiness during this life. Already in your daily life you are connected with what will be true in eternity, or to put it more exactly, what is already true of you in Christ. We think of the glory and perfection of heaven as future, which is accurate. And yet Hebrews, shortly after calling you to strive for holiness, informs you: “But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem… and to Jesus, the mediator of a new covenant, and to the sprinkled blood that speaks a better word than the blood of Abel” (12:22–24). Holiness characterizes the Christian both now (in a true and wonderful way) and in eternity (perfectly) — because Jesus is the crucified and risen Savior. To him be the glory forever!