Who are they, and from where did they come?

(John Angell James, "The Anxious Enquirer" 1834)

 After these things I looked, and behold, a great multitude,
 which no man could number, out of every nation and of all
 tribes, peoples, and languages, standing before the throne
 and before the Lamb, dressed in white robes, with palm
 branches in their hands. They cried with a loud voice,
 saying, "Salvation be to our God, who sits on the throne,
 and to the Lamb!" Revelation 7

Who are they that send forth such strains? Who are they,
and from where did they come?
"These are those who
came out of the great tribulation. They washed their robes,
and made them white in the Lamb's blood. Therefore they
are before the throne of God, they serve Him day and night
in His temple. He who sits on the throne will shelter them with
His presence. They will never be hungry, neither thirsty any
more; neither will the sun beat on them, nor any heat; for
the Lamb who is in the midst of the throne shepherds them,
and leads them to springs of waters of life. And God will
wipe away every tear from their eyes."

They were once upon earth; once men of like passions with
yourself. There is not a burden that oppresses your heart, but
oppressed theirs. There is not a fear that agitates your mind,
but agitated theirs. There is not a temptation that assails you,
but assailed them. There is not an obstacle that terrifies you,
but terrified them. They were once as ignorant, as weak, as
sinful, as timid, as discouraged, as you are now. There is
not a sorrow, a perplexity, or a danger with which you
are painfully familiar--but they passed through before you.

But there they are in heaven, more than conquerors over all
these things, through Him who loved them. He who saved
them has engaged to save you; nor is His ear heavy, nor His
arm shortened. "Therefore, since we are surrounded by so
great a cloud of witnesses, let us also lay aside every weight,
and sin which clings so closely, and let us run with endurance
the race that is set before us, looking to Jesus, the author
and perfecter of our faith, who for the joy that was set before
Him endured the cross, despising the shame, and is seated at
the right hand of the throne of God."