...With what forms of godliness, outward appearances, external embellishments are most people satisfied. How they mistake the shadows for the substance, the means for the end itself. How many devout Laodiceans are there who know not that they are ‘wretched and miserable, and poor and blind, and naked’ (Rev. 3:17). No preaching affects them, nothing will bring them to exclaim with the prophet, ‘O my God, I am ashamed, and blush to lift up my face to Thee my God’ (Ezra 9:6). No, if they do but preserve themselves from the known guilt of such sins as are punishable among men, to all other things their conscience seems dead: they have no inward shame for anything between their souls and God, especially not for the depravity and defilement of their natures: of that they know, feel, bewail nothing.
‘There is a generation that are pure in their own eyes, and yet is not washed from their filthiness’ (Prov. 30:12). Although they had never been cleansed by the Holy Spirit, nor their hearts purified by faith, (Acts 15:9), yet they esteemed themselves to be pure, and had not the least sense of their foul defilement. Such a generation were the self-righteous Pharisees of Christ's day: they were constantly cleansing their hands and cups, engaged in an interminable round of ceremonial washings, yet were they thoroughly ignorant of the fact that within they were filled with all manner of defilement (Matt. 23:25–28). So is a generation of churchgoers today; they are orthodox in their views, reverent in their demeanor, regular in their contributions, but they make no conscience of the state of their hearts.
That sanctification or personal holiness which we here desire to show the absolute necessity of, lies in or consists of three things. First, that internal change or renovation of our souls, whereby our minds, affections and wills are brought into harmony with God. Second, that impartial compliance with the revealed will of God in all duties of obedience and abstinence from evil, issuing from a principle of faith and love. Third, that directing of all our actions unto the glory of God, by Jesus Christ, according to the Gospel. This, and nothing short of this, is evangelical and saving sanctification. The heart must be changed so as to be brought into conformity with God's nature and will: its motives, desires, thoughts and actions require to be purified. There must be a spirit of holiness working within so as to sanctify our outward performances if they are to be acceptable unto Him in whom ‘there is no darkness at all.’ - A.W. Pink