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.
For the seasoned Christian soul, I do not see how it can be otherwise while people are perishing and we are saved. I do not see how it can be otherwise while these two passages are written by the same inspired man:
I have great sorrow and unceasing anguish in my heart. For I could wish that I myself were accursed and cut off from Christ for the sake of my brothers, my kinsmen according to the flesh. (Romans 9:2-3)
Rejoice in the Lord always; again I will say, Rejoice. (Philippians 4:4)