A quick intro regarding words:
Don’t get lost in the details! While more accurate meanings are very important, don’t get snagged by the assumption of the intellectual mind that perfect translation brings perfect understanding. Never forget, the very same religious mind that heard the actual words of Jesus still did not understand the truth of who he was or what he came to do, nor did it understand after he accomplished the will of his father.

Recap of Hebrews:
Many believers have come to view the letter of Hebrews as a mixed bag. For while we can reach into it and pull out some of the most wonderful statements of assurance regarding the nature of Jesus Christ and his finished work, we can’t help but come across those big IFs that seem to make every promise dependent upon our own persistence in the faith — whatever that may mean. Now, if we take the popular approach, we can selectively pick and choose the verses or passages we want to use and simply ignore the rest (and this holds true no matter where you’re coming from). Of course, we can always just avoid the letter, but does that keep the fear at bay … or do we just cover it over for a while?

Sooner or later the fear demanded by the fleshly religious mind shows up somewhere else. I’m telling you, the fear many of you believe to be hiding out in certain Hebrews verses isn’t actually caused by the letter of Hebrews, rather the letter simply stirs up what’s already hiding beneath the surface. And I’m not just talking about Biblical fears, I’m talking about the stuff that gives rise to those Biblical fears in the first place. After all, what has really driven all those fears in your life? In other words, did scary or uncertain Bible verses cause your fears or did they merely give those fears a place to call home? And the spirit of this world counts on and plays off these hidden or not-so-hidden fears. After all, fear and his two brothers, guilt and shame, represent some of the most powerful motivating forces in the world. Is it any surprise that preachers and teachers will capitalize on these powerful forces when they want to instigate change in those they deem apathetic Christians?

But what if Hebrews was not written to motivate apathetic Christians so as to get them off their blessed assurance and do something about it? What if instead it was written to those who had been called into the amazing grace of God, those who had in fact given of themselves because of the power of the new covenant, those who later found themselves paralyzed in the midst of an insanity of religious activity and ritual stirred up by fear and uncertainty? What if it was written to those whose faith was being undermined by the very community that called itself by the name of Christ? In other words, what if Hebrews had been written and consequently viewed as a declaration of certainty in the midst of uncertainty? You see, we’ve been taught to read Hebrews as if it was meant to add some kind of deeper dimension to our Christian life and faith — and because of this, those declarations of certainty have taken on different meanings. The truth of the matter is that Hebrews was written to challenge and expose the legalistic perversion of the new covenant that pretended to honor Jesus Christ and his sacrifice for sin while at the same time it denied the very reality of everything he was and did.

but Christ was faithful as a Son over His house–whose house we are, if we hold fast our confidence and the boast of our hope firm until the end. Hebrews 3:6 NASB
For we have become partakers of Christ, if we hold fast the beginning of our assurance firm until the end, Hebrews 3:14 NASB

There is a distinction I’ve been making that some of you may not be picking up on regarding the “hold fast” and the “IFs” in the Hebrews verses. While the “we” is true Israel (and are those who believe, and will continue to believe), I don’t see that as being the force behind his argument in these verses. Rather, he wants these believers to contemplate the nature of their confidence and the boast of their hope because that’s what was being challenged and called into question by the confrontation of the push for added sacrifices. The question before these Hebrews who believed was this: Is what you believed actually true? For if it was true, then they are Christ’s house and have become partakers of Christ.

The “truth” of the false Israel had twisted the assurance found in the phrase “whose house we are” into something more like, whose house we are trying to become. The joy in knowing that they had become partakers of Christ was being reformed before them as something more like, we are becoming partakers of Christ as we continue to keep ourselves clean with daily sacrifices. Now, maybe it wouldn’t have taken on phrasings of that nature, but I am certain the intimidation factor would have been demanding it, for the very essence of their former boasting in Christ was being eroded away according to the new teachings that were being accepted by so many.

What I’m saying is that the whole proposition before those who could actually hear the word of God was that they needed to consider the basic premise as put forth in their confidence, that is, in the truth which was contained within the boast of their hope. That confidence, that boast of their hope made a compelling case in view of what was being promoted by the mob. It demanded that they were already the house of Christ, that they had become partakers of Christ. And that’s why he wanted them to hold it fast firm until the end … but hang on for some more insight regarding this phrasing.

As I’ve brought up numerous times, the Greek εχω is translated mostly (like way mostly) as have. In fact, forms of hold only show up 15 times, while forms of have total over 550 occurrences. This is what leads me to regard a meaning closer of κατέχω to this: “to have according to”. The proposition he put forth tells them that if they have (or hold) Christ according to what their confidence demands that they already are Christ’s house, that they already have become partakers.
Now, it seems to be universally accepted that “until the end” refers to our believing, as if we have to maintain our faith in order to keep it going. I don’t recognize that as being true. I see the “until the end” as referring to the confidence, that is to the boast of the hope itself. In other words, while those Jews who had jumped on the Jesus-bandwagon gave his sacrifice an important place, as if it was needed to get their salvation rolling, the very reality of Christ in which true Israel had boasted declared that his sacrifice was the end of all sacrifices. Christ and him crucified is that which was “until the end”. It is the ultimate conclusion. If we truly have been made partakers according to Christ and his “until the end” sacrifice, then we are in fact right now partakers of him. If we do not have this according to his once-for-all sacrifice (that is, if more sacrifices are truly needed), then we are not partakers.