When someone says that God has not justified you eternally, what is meant by that? Never heard those two words together before.
1. There are those who hold to a doctrine called "Eternal Justification"; typically hyper-Calvinists. See
HERE and
HERE. It could be this person is denying that doctrine in which case he/she would be correct.
2. But if someone denies a justification that is eternal it
might indicate that the person has embraced Federal Vision, Shepherdism, or any of the myriad heresies which espouse a synergistic justification; grace/faith + works. I'm going to guess it is the former, FV, etc., which is making significant inroads in Reformed seminaries and thus in many Reformed churches. FV teaches that a person is initially 'justified' when they believe or they are baptized. Of course, their definition of 'justification' is NOT the biblical definition nor that held historically by the Church. Faith is simply a 'badge of identity' that you belong to the covenant people of God, the community of those who have professed faith in Christ, or children who have been baptized. You are said to be 'justified' at that time BUT you must maintain that status through being 'faithful to the covenant', i.e., keep the law. And IF you are faithful in keeping the law, then at the final judgment you will receive a second, final justification. Thus, your initial justification is not 'eternal' but temporary.
However, IF by some odd possibility this person believes that a person is NEVER justified eternally, i.e., you are eternally on a probationary status whereby you are held in good esteem by God if you live a perfect life, then that is an entirely different matter. That would be similar to the position which Adam was found before the Fall, aka: Covenant of Works.
Perhaps you need to ask the person, assuming it was an individual who spoke those words, to clarify what
they mean by them. If you read them in an article or book, then that may be a more difficult task to gain that information.