On the other side of ecstasy lies a painful emptiness.
On the other side of bitterness lies joy.
Where one goes, the other must follow.

In the ecstasy of understanding lies the gnawing pain of a new frontier of ignorance.

In the agony of yearning lies the ecstasy of love.

In the ecstasy of prayer lies the agony of smallness and distance before the infinite light.

There is no sweet song that is not equally bitter, save that which is shallow and meaningless.

He formed His world from delight, and so must share in its bitterness.
Until the time when the bitter will be sweet, when darkness will shine.

Rabbi DovBer of Lubavitch.