It was written by Thomas à Kempis, in "The Imitation of Christ", published in 1471.
Love feels no burden.
Thinks nothing of trouble.
Attempts what is above its strength.
Pleads no excuse of impossibility,
For it thinks all things lawful for itself, and all things possible.
It is therefore able to undertake all things,
And it completes many things and brings them to a conclusion,
Where he who does not love, faints and lies down.
Love watcheth, and sleeping, slumbereth not.
Though weary love is not tired
Though alarmed, it is not confounded,
But, as a lively flame and a burning torch,
It forces its way upwards,
and securely passes through it.
Nothing is sweeter than love,
Nothing more pleasant,
Nor better in Heaven and Earth;
Because love is born of God,
And cannot rest but in God above all created things.