John 16:21

When a woman is in labour she is sorry, for her time has come; but when the child is born she remembers her anguish no longer, for joy that a human being has been born into the world:

Revelation 7:14-17

I said to him, "You know, my lord." So he told me, "These are the people who have come out of the great Distress, who 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
When a woman is in labour she is sorry, for her time has come; but when the child is born she remembers her anguish no longer, for joy that a human being has been born into the world:
Revelation 7:14
I said to him, "You know, my lord." So he told me, "These are the people who have come out of the great Distress, who washed their robes and made them white in the blood of the Lamb.