Is the sealing of the saints in Revelation 7 something to happen in future only?

In the future..

And they are of the 144,000 the Bible does not call them Saints.. They are descendants of the 12 tribes of Israel.. Other scriptures in Revelation describe them as innocents having never known a woman..

And yes it will happen during the time of the wrath being poured out upon the earth at the times of the return of Jesus..

@Adstar They are called "servants ( δούλοις doulos) of God. They are obviously saints.
You are telling they are the people living in the time of end time wrath. If so, they are definitely called saints in many verses in the book of Revelation.

Read the given Bible portion above carefully.
At the time of John seeing the angel with the seal of God, he is on duty sealing those who are servants of God.
John heard the number who are already stamped from all tribes of Israel.
But from the words the angel with the seal, shouting to other four angels it is evident that he has not finished his task of sealing God's servants.
We can infer,
(1) The stamping of all the servants of God from all the tribes of Israel is completed.
(2) The angel has not completed his task of sealing saints of God.

It is evident that John is witnessing a scene which is ongoing but after completion of stamping servants of God with a reason "from one of the tribes of Israel".

No more servant of God is going to be added to the symolic number 144000 thereforth although angel with seal is still on his duty and mission of stamping servants of God of heaven.

John is brought to a vision which is to tell the saints of churches in Asia Minor that all the old testament saints are servants of God of heaven as with all the saints from New Testament age. (John 10:16)

These 144000 are then called "Those redeemed from among men, being the firstfruits unto God and to the Lamb. "
(Revelation 14:4, Gal 4:4, Jer 2:3)
If thease 144000 are tribulation saints, how can they accompany the Lamb (Rev14:1) on His onset for second coming while there are saints waiting for Him on earth? (Rev 24:12).
Please reply.

No harm in believing it if that's your choice, but we cannot know what the author really meant.

Its very exclusive, Israel-first message and colourful prose looks like a strange mixture of what we would call "nationalism", shamanism and its contemporary Judaic-tribal religion.

The inherent advantage of an undated "prophecy" is that it can recede into the future for ever-more! Those that are dated but fail, simply lapse into that section of History labelled "Errors and Eccentricities".

Remember the fuss and palaver about that Mayan calendar supposedly giving its own end time as early in the 21C? Or the imagined digital 1999/2000 apocalypse? Funny how their relevant years came and went without whatever was meant to happen, doing so!

How can it be done now, when we have all sinned??? Makes sense that God will want the most repenent for his tribe

It is during the tribulation. The 144 thousand are sealed and preach to the world.

I think it is 144,000 Jews that are saved during the great tribulation or at the end.

Well, it not happened yet, so the future seems to be the only option.

I believe so.