To "ransom" means to "rescue." This refers to people whom Yahweh has rescued. Alternate translation: "Those whom Yahweh has rescued" (See: [[rc://en/ta/man/translate/figs-nominaladj]])
This uses a person's head to mean the person as a whole. Alternate translation: "they will be glad forever" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
The words "gladness" and "joy" mean basically the same thing, as do "sorrow" and "mourning." Together they emphasize the intensity of these emotions. (See: [[rc://en/ta/man/translate/figs-doublet]])
This speaks of the people being overwhelmed by gladness and joy by giving these emotions the human quality of being able to overtake someone. Alternate translation: "they will be overwhelmed by joy and gladness" or "they will be extremely glad and joyful" (See: [[rc://en/ta/man/translate/figs-personification]])
This speaks of the people no longer being sorrowful and mourning by speaking of these emotions as if they could run away. Alternate translation: "they will no longer be sorrowful and mourning" (See: [[rc://en/ta/man/translate/figs-personification]])