If we are sanctified, we are perfected forever  -  Hebrews 10:14

For by one offering he hath perfected for ever them that are sanctified.

Those that are sanctified means all who have been set apart to God from the world. They have been perfected in a two-fold sense – 1) they have a perfect standing before God because of their salvation through Jesus Christ, 2) they have a perfect conscience as far as the guilt and penalty of sin are concerned, as the price for sin has been paid in full.