Perfected by One Sacrifice
Heb 10:11-14 Day after day every priest stands and performs his religious duties; again and again he offers the same sacrifices, which can never take away sins. But when this priest had offered for all time one sacrifice for sins, he sat down at the right hand of God. Since that time he waits for his enemies to be made his footstool, because by one sacrifice he has made perfect forever those who are being made holy.
Again "one sacrifice" as opposed to Catholicism's weekly sacrifice of the Mass.
Ps 110:1 The LORD says to my Lord: "Sit at my right hand until I make your enemies a footstool for your feet." This is the same Psalm which contains the verse The LORD has sworn and will not change his mind: "You are a priest forever, in the order of Melchizedek." and which Jesus referenced in Luke 20:42,43 and Peter in Acts 2:34,35 as referring to the Messiah.
He sits because his work is done, having been accomplished on the cross. Notice the tense in the phrase, "has made perfect forever" Those who are in Christ have in one sense already been made perfect, and not only so but "forever" indicates that such a state is permanent, which affirms the concept of Eternal Security (once saved, always saved). And this again is in contrast to the Old Covenant which as he said in the first verse of this chapter that such sacrifices under that covenant cannot make perfect those who draw near to worship. There is no eternal security under the Old Covenant.
But there is still a process of "being made holy" to which those born of God are subject. But as the grammar shows, it's passive, it's what's done to the believer as opposed to the various Neo-Circumcision sects in which one continues to try to maintain their salvation status through right behavior and where holiness is not inevitable. They still live under the Law.