So basically when Christ said "It is finished" He didn't really mean it. When Hebrews said that "he hath by one offering perfected forever them that are sanctified" the scriptures didn't really mean it. That's essentially what you are saying.
While it is true that Christ's work as high priest didn't end at the cross, His atoning work did. The atonement was finished with that one sacrifice.
Correction.
1. The "Atoning Sacrifice" (NIV 1John 2:2) was finished "once for all" at the cross by His once for all sacrifice for sins. An "Atoning Sacrifice for OUR sins and NOT for OUR sins only but for the sins of the WHOLE WORLD" 1John 2:2.
2. In God's own definition of "Atonement" given in Lev 16 "Day of Atonement" - it does not "end" when the sin offering is "slain" -- but rather it continues with the work of High Priest until the entire "process" is ended - the full meaning of "Atonement" is not yet complete. No sense in arguing with the text at that point.
3. In Heb 7 and 8 Christ is seen to take up that role as our High Priest at His ascension into heaven.
In Heb 9 He is seen doing the work as our High Priest in heaven's sanctuary.
In 1John 2:1 "we have an advocate with the Father" if we sin.
In 1John 1:9 - our advocate not only provides forgiveness of sins but also "cleansing".
4. With the ongoing work of Christ "included" in the broader Biblical concept of atonement (instead of just limiting the meaning to "Atoning Sacrifice" which all agree was completed at the cross) - we see how it is that the sacrifiice can be "NOT for OUR sins only but for the sins of the whole world" AND YET the whole world is not saved.
As far as the whoever comes to Christ, the bible tells us that the only ones that will come to Christ are those drawn by the Father.
John 12:32 "I will draw ALL unto Me" the term is unqualified -- it is the unqualifiied ALL that are drawn.
John 16 He "convicts the WORLD of sin and rightousness and judgment".
John 1 "He is the light of the world and coming into the world He enlightens every one of mankind".
2Peter 3 "He is not willing for ANY to perish but for ALL to come to repentance".
As far as the refusing of the gospel goes, the problem with your idea is that not all have heard the gospel. What do you do with them?
He enlightens EVERY man.
He draws ALL unto Him.
Romans 2 -- for even the gentiles who do NOT have scripture are a law unto themselves -- showing that they have the New Covenant promise of the Law written on the heart.
Romans 10 asks the very question "surely they have never heard have they?" And then Paul makes the case from Psalms "indeed they have" - for nature itself (from the psalms) speaks of the God of creation.
Paul says in Romans 1 that even barbarians can see the "invisible attributes of God clearly seen in the things that have been made".
in Christ,
Bob