Basil of Caesarea

The joy of God is not found in just any soul but, if someone has mourned much and deeply his own sin with loud lamentations and continual weepings, as if he were bewailing his own death, the mourning of such a one is turned into joy.… The mourning garment, which he put on when bewailing his sin, is torn, and the tunic of joy is placed around him and the cloak of salvation, those bright wedding garments, with which if one is adorned, he will not be cast out from the bridal chamber.

HOMILIES on the PSALMS 14:7 (PS 30)

Augustine of Hippo

"You have turned My mourning into joy to Me" [Psalm 30:11]. Whom I, the Church, having received, the First-Begotten from the dead, [Revelation 1:5] now in the dedication of Your house, say, "You have turned my mourning into joy to me. You have put off my sackcloth, and girded me with gladness." You have torn off the veil of my sins, the sadness of my mortality; and hast girded me with the first robe, with immortal gladness.

Exposition on Psalm 30 ↗

Thomas Aquinas

He explains the manner when he says, "You have turned." Insofar as he speaks of Christ, he says two things. For first he shows the change from evils to good, as to interior things. Second, as to exterior things, at "You have torn." Christ had mourning at the time of the passion in himself: because "My soul is sorrowful," etc. Mt. 26. And in his own: Jn. 16: "Because you shall weep and lament," etc. "You have turned this mourning," he says, "into the joy" of the resurrection. As to himself: Ps. …

Exposition on the Psalms of David ↗