Terminal Salvation

To help us make more sense of our position “in Christ”, here are some thoughts concerning its legal underpinnings.
 
First off, let’s see how you “got into” Christ.  A person gets baptized (a much more exact meaning of the word is “immersed, with lasting effects”) into Christ the moment they believe in him: 
 

Mark 16:16
16 He who believes and is baptized will be saved; but he who does not believe will be condemned.

 
Here are some verses describing a believer as having been been baptized (a much more exact meaning of the word is “immersed, with lasting effects”) into Christ:

1 Corinthians 12:12-13
12 For as the body is one and has many members, but all the members of that one body, being many, are one body, so also is Christ. 13 For by one Spirit we were all baptized into one body—whether Jews or Greeks, whether slaves or free—and have all been made to drink into one Spirit.

Romans 6:3-4
3 Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death? 

Galatians 3:26-27
26 For you are all sons of God through faith in Christ Jesus. 27 For as many of you as were baptized into Christ have put on Christ.

Notice how it doesn’t talk about water at all here.  The substance into which you are immersed is Christ, not water.  Water was a shadow, the substance is Christ!
 
Now we come to Abraham and Melchizedek.
 

Hebrews 7:4-10
4 Now consider how great this man was, to whom even the patriarch Abraham gave a tenth of the spoils. 5 And indeed those who are of the sons of Levi, who receive the priesthood, have a commandment to receive tithes from the people according to the law, that is, from their brethren, though they have come from the loins of Abraham; 6 but he whose genealogy is not derived from them received tithes from Abraham and blessed him who had the promises. 7 Now beyond all contradiction the lesser is blessed by the better. 8 Here mortal men receive tithes, but there he receives them, of whom it is witnessed that he lives. 9 Even Levi, who receives tithes, paid tithes through Abraham, so to speak, 10 for he was still in the loins of his father when Melchizedek met him.

 
You see here that Levi, not being born yet, paid tithes through Abraham, because Levi was Abraham’s descendant.  (“so to speak” in v. 9 doesn’t mean it’s figurative; literally it says “say to be saying” – i.e. “what I am trying to say”).  So Levi gave tithe through Abraham simply because he was in Abraham’s loins – i.e., he was Abraham’s descendant.  So this specific tithing action done by Abraham was set to Levi’s credit.  Furthermore, if you compare v. 9 with v. 5 – you see that Levi is identified with his own descendants, or “sons of Levi”.  So now we see how sons of Levi being in Levi, who was in turn in Abraham, tithed to Melchizedek, through Abraham’s one-time act.
 
Let’s take another example.  Consider Romans 5:17-19 (most translations really mangle v. 18, so I quote it in Young’s Literal):

Romans 5:17-19
17 for if by the offence of the one the death did reign through the one, much more those, who the abundance of the grace and of the free gift of the righteousness are receiving, in life shall reign through the one — Jesus Christ.
18 So, then, as through one offence to all men to condemnation, so also through one declaration of `Righteous’ to all men to justification of life;
19 for as through the disobedience of the one man, the many were constituted sinners: so also through the obedience of the one, shall the many be constituted righteous.

Adam and Jesus contrasted here.  I was a sinner because I was “in Adam” (including in the spirit part of my being).  v. 19 – I became a sinner as the result of Adam’s disobedience.  v. 19 – I became righteous through Christ’s obedience, the moment I was taken out of Adam and placed (baptized) into Christ.  (In this passage, by the way, the reader’s understanding of what it means to be placed into Christ is assumed – otherwise it won’t make sense).  All I had to do is believe on Christ.  
 
You see how this changing of my spiritual lineage had such a profound effect?  By simply being put into (baptized into, immersed into) Christ, I gained access to all Jesus has done!  It has nothing to do with my actions, it has everything to do with me being in a specific lineage.  Actions do matter in a lot of other contexts, to be sure, but our deeds are powerless to place us into Christ, hence the need for outside help (namely, from God himself).
 
So in the same (actually, in an even deeper) way as Levi tithed to Melchizedek since he was in Abraham (while yet unborn), now that I got into Christ through faith – I can confidently say (Pauline revelation confirming every single point of this sequence as directly applicable to me) that I have been judged, condemned, crucified, and died with Christ on the cross in Judea 2000 years ago, and was then justified (specifically, in the spirit), rose again, and sat at the right hand of the father.  
 
For instance, in Greek Gal 2:20 says “I have been co-crucified (sunestauromai, in perfect passive tense) with Christ”.  I didn’t have to carry my own cross and follow Jesus to the place of death.  He did even that for me.  Now that I am in Christ, that’s now all done for me, and is mine.  
 
Notice the sun/sum prefix in the Greek verbs.  It points to togetherness (or simultaneity).  In English we have Greek loanwords that make use of this prefix, such as symphony (together-sound), synergy (together-work), etc.  
 
Here are 2 more passages regarding this:
 

Colossians 2:11-14
11 In Him you were also circumcised with the circumcision made without hands, by putting off the body of the sins of the flesh, by the circumcision of Christ, 12 buried (suntaphentes – co-entombed, aorist passive) with Him in baptism, in which you also were raised with Him (sunegerthete – co-raised-up, aorist passive) through faith in the working of God, who raised Him from the dead. 13 And you, being dead in your trespasses and the uncircumcision of your flesh, He has made alive together (sunezoopoiesen – co-makes-alive, aorist active) with Him, having forgiven you all trespasses, 14 having wiped out the handwriting of requirements that was against us, which was contrary to us. And He has taken it out of the way, having nailed it to the cross.

Ephesians 2
4 But God, who is rich in mercy, because of His great love with which He loved us, 5 even when we were dead in trespasses, made us alive together with Christ (sunezoopoiesen – co-makes-alive, aorist active) (by grace you have been saved), 6 and raised us up together (sunegeiren – co-raises-up, aorist active), and made us sit together (sunekathisen – co-seats, aorist active) in the heavenly places in Christ Jesus,

 
and so on.  Verb tenses, being mostly aorist, give an additional level of insight into the idea that all these things are a state of being for us.  
 
As a side note, an important takeaway from this is that what is commonly referred to as “salvation” is not “a thing”, but a series of transformational events that happen in established sequence to every person who places their trust in Christ, although such events are not physically perceptible.
 
Now we come to this.  There is a promise of God to Abraham concerning his heirship of the world.  Paul talks about this in Romans:

Romans 4:13
13 For the promise that he would be the heir of the world was not to Abraham or to his seed through the law, but through the righteousness of faith.

 
The promise was to Abraham – and consequently his descendants, through Isaac (child of promise – Heb 11:18, as opposed to child of flesh / self-effort).  Since no Gentile was a direct descendant of Abraham, that specific promise couldn’t cover Gentiles before Christ came to earth.  Now, since Christ was in Abraham’s lineage via Isaac, the promise was to Christ.  Christ appropriated the promise of heirship, the Holy Spirit was then sent to empower the physical realization of it.  Now, get this – since we are in Christ, and Christ is in Abraham, we are now in Abraham via Christ, and the promise of heirship of the world made to Abraham and his seed personally is now ours. 

Genesis 22:18
18 In your seed (i.e., Christ – seed is singular here – see Gal 3:16) all the nations of the earth shall be blessed, because you have obeyed My voice.” (i.e., obeyed God’s command to sacrifice Isaac – this verse was directly following Abraham’s (near-)sacrifice of his son.)

Galatians 3:14, 16, 26,27,29

14 that the blessing of Abraham might come upon the Gentiles in Christ Jesus, that we might receive the promise of the Spirit through faith.

16 Now to Abraham and his Seed were the promises made. He does not say, “And to seeds,” as of many, but as of one, “And to your Seed,” who is Christ.

26 For you are all sons of God through faith in Christ Jesus. 
27 For as many of you as were baptized into Christ have put on Christ. 

29 And if you are Christ’s, then you are Abraham’s seed, and heirs according to the promise.

 
You see, the iron-clad legal underpinning of this issue is such that no Gentile could partake of Abraham’s blessing before they could get into Abraham via Christ, and no human could get out of sinful Adam until they could get into a sinless human, that is Christ.  It took thousands of years (roughly 2 and 4, respectively) in both cases, and it couldn’t be done sooner that it did.  It had to be done right.  But now that it’s done, it’s really done!  The long wait was well-worth it.
 
Here’s one last point.  God didn’t just bless me for nothing by giving Jesus up for me.  Abraham gave up Isaac for God, Isaac was as good as dead in God’s eyes (or if you want to co-opt Shrödinger’s cat experiment terminology – Isaac was both dead and alive at the same time, God simply let the scenario where he was alive to materialize by stopping Abraham at the last moment).  Since Abraham sacrificed his son, and I am in Abraham through Christ, that act is now set to my account.  So I can say that “I gave my son, my only son that I love” up for God through Abraham, so that God could do the same for me.  So as far as satan “the Accuser” is concerned, there’s absolutely no ground for accusation that God blessed me undeservedly.  He (satan) used a variation of this accusation on Job (1 Job 1:9), but for the above reason that particular accusation has no standing in my case, since I am in Abraham.  (Well, my situation is nothing like Job’s – I am in an awesome covenant with God through Christ, I have an advocate with the Father, etc. – but I want to hit that particular point, that God’s gift of crucified Christ was set up as bulletproof to potential legal challenges from very early on).
 
SO, God is 100% justified to have blessed us with every spiritual blessing in Christ Jesus.