It is not a sign of a seasoned Christian soul that steady joy is untinged with steady sorrow.
Or to put it positively, the seasoned soul in Christ has a steady joy and a steady sorrow.
They protect each other. Joy is protected from being flippant by steady sorrow. Sorrow is protected from being fatal by steady joy.
And they intensify each other. Joy is made deeper by steady sorrow. Sorrow is made sweeter by steady joy.
From John Piper at Desiring God