A "Must-Have" Holiness

Strive for peace with everyone, and for the holiness without which no one will see the Lord. (Hebrews 12:14, ESV)
Jerry Bridges writes on this sobering verse:
“So the writer of Hebrews is telling us to take seriously the necessity of personal, practical holiness. When the Holy Spirit comes into our lives at salvation, He comes to make us holy in practice. If there is not, then, at least a yearning in our hearts to live a holy life pleasing to God, we need to seriously question whether our faith in Christ is genuine…
The whole purpose of our salvation is that we be ‘holy and blameless in his sight’ (Ephesians 1:4). To continue to live in sin as a Christ is to go contrary to God’s very purpose for our salvation. One of the writers of three centuries ago  [Walter Marshall] put it like this: ‘What a strange kind of salvation do they desire that care not for holiness . . . They would be saved by Christ and yet be out of Christ in a fleshly state . . . They would have their sins forgiven, not that they may walk with God in love, in time to come, but that they may practice their enmity against Him without any fear of punishment.’”
The Pursuit of Holiness, p. 33-34