To him that overcometh will I grant to sit with Me in My
throne, even as I also overcame, and am set down with
My Father in His throne (Revelation 3:21).
After this I beheld, and, lo, a great multitude, which no
man could number, of all nations, and kindreds, and people,
and tongues, stood before the throne, and before the
Lamb, clothed with white robes, and palms in their
hands…(robes and palms speak of Redemption and Salvation)
 (Revelation 7:9)

In the Book of Revelation, there are two classes of Believers.

The first is The Overcomer.

The Overcomer is The Bride of Christ whom He has chosen. 
It is all those who went further with The Lord, beyond their
salvation and responded to the High Calling in Christ and
are seated with Christ in His throne. A people called of God
to more. Who loved not their lives unto death. Who rose
above their life circumstance and  overcame, who followed
The Lamb wherever He went. A Bride who has "made herself ready"
for The Marriage Supper of The Lamb".

The Second is The Multitude.

Therefore are they (the multitude) before the throne of God,
and serve Him day and night in His temple: and He that
sitteth on the throne shall dwell among them…(Revelation 7:15)

For the Lamb which is in the midst of the throne shall feed
them (the multitude), and shall lead them unto living fountains of
waters: and God shall wipe away all tears from their eyes
(Revelation 7:17).

There is a vast multitude that stands before His Throne.
They received of The Lord during their life the free gift of Salvation.
Heaven is their home for all eternity.

As they stand in the presence of The Lord and see all those who overcame
that are seated with Him they begin to weep and cry with a loud voice
because now they realize that they missed the opportunity to be an
overcomer and be chosen as His Bride. They spent their lifetime
accumulating riches in this world and being concerned for temporary 
things and the cares of this world but failed to purchase eternal things.

Revelation 12:11
And they overcame him by the blood of the Lamb,
and by the word of their testimony;
and they loved not their lives unto the death.

Our testimony is the expression of our relationship with The Lord.
It is the accumulation of all the decisions that we have made over
our lifetime that have registered and formed our "Eternal Expression".
The Multitude was freely given Salvation but did not grow during
their lifetime but chose their own way and the way of the world and
never submitted their lives to His Lordship.

The Overcomer during their lifetime allowed The Lord to bring them into a
special relationship where they became a “Living Sacrifice" unto The Lord.
Their self-life was dealt with by the daily working of The Cross and
was no longer an obstacle or hindrance to the expression of His Life. They are
the “Wise Virgins”, Their lamps were full of oil which speaks of direct
and ongoing communion with The Bridegroom.

The time that we have, here on earth, is the most important time of all eternity,
as we are making our decisions for eternity now.  This is the reason The Multitude shed bitter tears. 
They saw what could have been, as they "stand" before the throne and see the overcoming Bride
"seated" with The Lord.

John 12:25 He that loveth his life shall lose it; and
                    he that hateth his life in this world shall keep it unto life eternal

If we love our life here we will lose something of eternal value there...........

The unspeakable Joy of having an intimate relationship with Our Lord as His Bride for all Eternity.
A Joy unspeakable and fullness of Glory as we rule and reign with Our Lord as His Sons for all Eternity.

“I press toward the mark for the prize of the high calling of God in Christ Jesus.”  Philippians 3:14

“And he that overcometh, and keepeth My works unto the end,
to him will I give power over the nations: And he shall rule them with a rod of iron; ....
He that hath an ear, let him hear what the Spirit saith unto the churches.” –Revelation 2:26-29

Paul saw the difference in these groups, and he sought the higher level (high calling of God).
May we also seek this eternal relationship of being seated with Jesus in His throne, as a Bride and a Son having

"Overcome this world even as He Overcame"

Our Lord will surely "wipe away the tears" of the multitude and "dwell" among them.
However those are tears that we never need shed as Today we can come before Jesus
and "surrender our lives" to Him and allow Him to take us far beyond our Salvation and
prepare us as His Bride. This is the very heartbeat of The Lord as He sits enthroned beside
The Father ever making intercession for us that we would be engaged to Him with eyes for
Him only and "enter in " so that on "that day" our place will be at The Marriage Supper of The Lamb