John Gill Commentary Psalms 51:8

"Make me to hear joy and gladness, That the bones which thou hast broken may rejoice." — Psalms 51:8 (ASV)

Make me to hear joy and gladness
Which he had not heard for some time; sin had sadly broke in upon and interrupted his spiritual peace and joy; for though the love and favour of God cannot be lost, yet his sensible presence, which puts joy and gladness into the heart, may; and though an interest in Christ ever continues, and union to him is always the same; yet a view of interest in him, which fills with joy unspeakable and full of glory, and communion with him, may not be had for a time; and though justification by his righteousness, from whence flows much peace, is an invariable blessing; yet the comfortable perception of it may be taken away; and though salvation by Christ is a certain thing, yet the joy of it may be lost for a season; which was now the case of the psalmist.

And when he desires that God would cause him to hear joy and gladness, his meaning is, that he might have that made known unto him; namely, the forgiveness of his sins, which would give him joy: not by an articulate voice from heaven, which he did not expect; nor by an angel from thence, which was not usual; but by the prophet, who as yet might not have declared to him that God had put away his sin; or, if he had, he might desire to have it repeated, for his fuller assurance, and greater joy; or by his Spirit, in an impulse on his mind, saying to him, your sins are forgiven you; which would give him great joy, fulness of it, even what is inconceivable and inexpressible, signified by these two words, "joy" and "gladness";

[that] the bones [which] you have broken may rejoice :
a backsliding believer is not only like a bone out of joint, (Galatians 6:1) ; but his falls are sometimes both to the bruising of him, and to the breaking of his bones; of which when he is sensible, the quick sense of his sin is as the pain of a broken bone; see (Psalms 38:3Psalms 38:6Psalms 38:8Psalms 38:9) ; and here the breaking of them is ascribed to God; not that he is the cause or occasion of falling into sin, which breaks the bones, (James 1:13) ; but of afflictions, corrections, and chastisements for sin, which are sometimes expressed by this phrase, (Isaiah 38:13) (Lamentations 3:4Lamentations 3:16) ; and of the menaces and threatenings of the law, which being let into his conscience, worked wrath and terror there; and also of that true contrition of heart, and brokenness of spirit, which the Lord produces.

And can only cure, by the discoveries of pardoning grace; which affects the whole frame of nature, the report of which makes the bones fat, and all of them to say, who is a God like unto you? (Proverbs 15:30) (Psalms 35:9Psalms 35:10) .