To answer your question we need to have a look what was happening in the world prior to the scripture in question.
Blessed are the dead who die in the Lord from now on
The world at this time (according to scripture), is in a bad way.Revelation 14:6-7 explains what is happening,
The Three Angels
6 Then I saw another angel flying in midair, and he had the eternal
gospel to proclaim to those who live on the earth—to every nation,
tribe, language and people. 7 He said in a loud voice, “Fear God and
give him glory, because the hour of his judgment has come. Worship him
who made the heavens, the earth, the sea and the springs of water.”
The OP asks,
"What's so special about those who die from now on? What about the ones who died before"?
The opening of the fifth seal reveals important information regarding the ones who died before and also the ones who are yet to die, (namely), the blessed ones of Rev 14:13.
Revelation 6:9-11
9 When he opened the fifth seal, I saw under the altar the souls of
those who had been slaughtered for the word of God and for the
testimony they had given; 10 they cried out with a loud voice,
‘Sovereign Lord, holy and true, how long will it be before you judge
and avenge our blood on the inhabitants of the earth?’ 11They were
each given a white robe and told to rest a little longer, until the
number would be complete both of their fellow-servants and of their
brothers and sisters, who were soon to be killed as they themselves
had been killed.
It is altogether grim reading and a time when many people hope that they will not be a part of this scene of life in their life time, but the scriptures do give encouragement to the believers of Rev 14:13 because it is recorded at Revelation 14:12,
This calls for patient endurance on the part of the people of God
who keep his commands and remain faithful to Jesus.
And there is a blessing to be had by the believers, by way of holding to the above scripture which takes Revelation 22:7 into focus and gives encouragement to the believers
‘See, I am coming soon! Blessed is the one who keeps the words of the
prophecy of this book.’
Revelation 14:13
And I heard a voice from heaven saying, ‘Write this: Blessed are the
dead who from now on
die in the Lord.’ ‘Yes,’ says the Spirit, ‘they
will rest from their labours, for their deeds follow them.’
‘Yes,’ says the Spirit, ‘they will rest from their labours, for their deeds follow them.’
The above scripture "strongly" alludes to the book of Hebrews at chapters 3 and 4 and starts to pick up on the meaning when the spirit starts speaking at Hebrews 3:7-8
Hebrews 3:7-8
Warning against Unbelief
Therefore, as the Holy Spirit says, ‘Today, if you hear his voice, do
not harden your hearts as in the rebellion, as on the day of
testing in the wilderness,
And then comes a promised blessing after death comes,
Hebrews 4:1-3
The Rest That God Promised
Therefore, while the promise of entering his rest is still open, let
us take care that none of you should seem to have failed to reach it.
For indeed the good news came to us just as to them; but the message
they heard did not benefit them, because they were not united by faith
with those who listened. For we who have believed enter that rest,
just as God has said, ‘As in my anger I swore, “They shall not enter
my rest” ’, though his works were finished at the foundation of the
world.
Hebrews 4:9-10
9 So then, a sabbath rest still remains for the people of God; 10 for
those who enter God’s rest also cease from their labours as God did
from his.
Note the similar wording of Rev 14:13,
Yes,’ says the Spirit, ‘they will rest from their labours, for their deeds follow them.’
Conclusion
"What's so special about those who die from now on? What about the ones who died before"?
The ones who died before are (Also) truly blessed, because they have rested from their labour and are with their Father in heaven, Rev 6:9-11. Then they were each given a white robe and told to rest a little longer,
The ones who die from now on are truly blessed because they hold to the words of Jesus and keep to the words of the prophecy of the book of Revelation in a severe time of testing.
This calls for patient endurance on the part of the people of God who keep his commands and remain faithful to Jesus.
Blessed are the dead who die in the Lord from now on.