Jesus Christ stood in the place of Adam, there is a complete unity of both. If Christ did not in fact provide universal atonement, Christ would not be made as the comparison or stand-in for Adam, as it would in fact only be a part of Adam. Adam has a unity, he comes as a whole, he is the federal head. This is why Jesus buys the whole field only to get the treasure inside it, and why as in Adam all die, so only in Christ can any be made alive.
But please take a look at this passage with me that disproves Eternal Justification:
11 Therefore remember that you, once Gentiles in the flesh-- who are called Uncircumcision by what is called the Circumcision made in the flesh by hands--
12 that at that time you were without Christ, being aliens from the commonwealth of Israel and strangers from the covenants of promise, having no hope and without God in the world.
13 But now in Christ Jesus you who once were far off have been brought near by the blood of Christ. (Eph. 2:11-13 NKJ)
Now the phrase I want you to really hone in on is this one: "at that time you were without Christ." Under Eternal Justification, it is a logically impossibility for any elect to be at any time "without Christ." For clearly we can pull up a hundred passages that tell us that only in Christ are we justified, forgiven, chosen, etc. Yet, these who have been brought near were without God and outside the covenant.