They have washed their robes and made them white in the blood of the Lamb.@Revelation 7:14
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Fanny Crosby (1820–1915)

Fan­ny Cros­by, 1906 (🔊 pdf nwc). We nor­mal­ly think of Fan­ny Cros­by as a lyr­i­cist, but for this hymn she is cred­it­ed with writ­ing the mu­sic, as well. It is all the more re­mark­a­ble be­cause she was 86 years old at the time.

There is a blood-washed multitude, a mighty army strong;
The Lord of hosts their righteousness, redeeming love their song.
They follow Christ whose name they bear, to yonder portals bright,
Where He has said His faithful ones shall walk with Him in white.

That precious name their guiding star, its beams will o’er them cast,
And through its power their trusting souls shall overcome at last.
The glory cloud will bring them safe to yonder palace bright,
Where they shall see Him eye to eye and walk with Him in white.

March on! O blood-washed multitude, for lo! the hour draws nigh,
When we shall hail the King of kings triumphant in the sky.
When songs of praise to Him we love, shall fill the courts of light,
And they that overcome the world, shall walk with Him in white.