The context shows he means we're to comfort each
other that we'll see our loved ones again, and that all
of us -- no matter whether we live or die -- will be
resurrected or raptured at Christ's coming:

1 Thes 4:13-18
But I would not have you to be ignorant, brethren,
concerning them which are asleep, that ye sorrow not,
even as others which have no hope. For if we believe
that Jesus died and rose again, even so them also which
sleep in Jesus will God bring with him. For this we say
unto you by the word of the Lord, that we which are alive
and remain unto the coming of the Lord shall not prevent
them which are asleep. For the Lord himself shall descend
from heaven with a shout, with the voice of the archangel,
and with the trump of God: and the dead in Christ shall
rise first: Then we which are alive and remain shall be
caught up together with them in the clouds, to meet the
Lord in the air: and so shall we ever be with the Lord.
Wherefore comfort one another with these words.

Paul didn't mention the tribulation here because
tribulation and comfort aren't opposed to each other:

2 Cor 1:3-7
Blessed be God, even the Father of our Lord Jesus
Christ, the Father of mercies, and the God of all
comfort; Who comforteth us in all our tribulation,
that we may be able to comfort them which are in any
trouble, by the comfort wherewith we ourselves are
comforted of God. For as the sufferings of Christ
abound in us, so our consolation also aboundeth by
Christ. And whether we be afflicted, it is for your
consolation and salvation, which is effectual in the
enduring of the same sufferings which we also suffer:
or whether we be comforted, it is for your consolation
and salvation. And our hope of you is stedfast, knowing,
that as ye are partakers of the sufferings, so shall
ye be also of the consolation.

This makes clear our comfort isn't based on our
deliverance from physical tribulation, but on our close
relationship with Christ, and on the indestructible
spiritual hope He gives us of resurrection and eternal
life at His appearing:

1 Cor 15:54-55
So when this corruptible shall have put on incorruption,
and this mortal shall have put on immortality, then shall
be brought to pass the saying that is written, Death is
swallowed up in victory. O death, where is thy sting?
O grave, where is thy victory?
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