Matthew 10:15 speaks of the future Day of Judgment in which all people will stand before God, the righteous being commended and the unrighteous being condemned in the final eschatological sense. See: (Matthew 25:31-46)
John 3:18 speaks to the current state of affairs that the unregenerate are currently persisting in. In other words, they refuse to believe in the name of the only Son of God by which they may be saved.
Such an impenitent continuous action on part of those who are atheistic or agnostic in their way of life is what makes them criminals before God, before judgment day.
Romans 1:18-32 shows that mankind knows of God’s existence but they stifle that general revelation which in turn provokes God’s wrath against them: (Romans 1:18-22).
God is angry even before the “day of wrath”(Rom 2:5), because He commands all men everywhere to repent (Acts 17:30) and He has appointed a day when He will judge the world in righteousness by Jesus Christ: (Romans 2:16)
The comparison between Matthew 10:15 and John 3:18 is one of rebels who refuse to repent & believe in Christ for their own salvation, and are held accountable here and now. They store up for themselves wrath by persisting in unbelief.
Scriptures to consider:
Romans 1:18-Chapter 3:20 (AKA God’s lawsuit against humanity), Acts 17:22-31.
God holds men accountable for their refusal to repent:
“The rest of mankind, who were not killed by these plagues, did not
repent of the works of their hands, so as not to worship demons, and
the idols of gold and of silver and of brass and of stone and of wood,
which can neither see nor hear nor walk; and they did not repent of
their murders nor of their sorceries nor of their immorality nor of
their thefts.” Revelation 9:20-21
CONCLUSION: There is an already & not yet for condemnation, since all are sinners in Adam: (Romans 5:12-21).
