John 16:21

A woman when she is in labor, hath sorrow, because her hour is come; but when she is delivered of the child, she thinks no more of the anguish, for joy, that a man is born into the world.

Revelation 7:14-17

And I said unto him, Sir, thou knowest. And he said to me, These are they who come out of great affliction, and have washed their robes, and made them white in the blood of the Lamb.

Treasury of Scripture Knowledge

Summary

Because thou shalt forget thy misery, and remember it as waters that pass away:

Bible References

Because

John 16:21
A woman when she is in labor, hath sorrow, because her hour is come; but when she is delivered of the child, she thinks no more of the anguish, for joy, that a man is born into the world.
Revelation 7:14
And I said unto him, Sir, thou knowest. And he said to me, These are they who come out of great affliction, and have washed their robes, and made them white in the blood of the Lamb.