When we are unaware of the gospel we are ignorant of the true nature of God and his character. We don’t know what he wants of us and what we are.
But, when we join his family we are awakened to a new position. We have the same body, but our thinking and belief and will have been altered. Then, Jesus starts and speaks through the Holy Spirit and we begrudge what He exposes in us. ‘ I never felt or heard that in my life’ we argue. But now we are ‘set apart, separate (holy in Hebrew) we are people of the light.
That does not mean we are moral people, because people can be moral and not holy.
Holiness is belonging to God. That means that we live for him and not for ourselves. That means that our minds, hearts and will are tuned to his and we forever looking and listening to him.
It might sound hard, sometimes it is hard, but holiness is joyful living.
( See 1 Corinthians 3:16-20, 2 Timothy 1:9, Philippians 2:13)