"Like one who takes off a garment on a cold day, or like vinegar on soda, is he who sings songs to a trouble heart."
no garment on a cold day
The word garment is the Hebrew word beged, which is the standard word for clothing. The idea here is that it is not normal or advisable to take off garments on cold days.
vinegar on soda
The foaming, expanding reaction of vinegar and soda tells people that these two substances should not be mixed.
The above two examples are used to point out things that shouldn't be together and so this third example is the point of the proverb.
sings songs
The word translated song here is the word sir in Hebrew. It is used for all kinds of songs: worship songs, secular songs, festive songs, etc.
troubled
This is the key word in this proverb; it is the Hebrew word ra which means evil. The translators chose the word troubled to reflect that one's soul can be out of sorts; that it cannot be where it should be. Most commentators – both ancient and modern – did not attribute actual evil actions to the soul in this proverb. They were looking for something out of place or something which clearly did not fit together and singing cheery, happy songs to a depressed or churning soul is a mistake.
It is also possible that ra means evil in the sense that a person's soul can be bent on doing that which God calls evil and, therefore, when a person tries to sing songs to a person bent on doing that which is morally reprehensible, it is incompatible. The idea here is that it is a mistake to make nice and happy to a person bent on doing evil. It is incompatible. If you know of someone who is bent on doing that which is evil or someone who is brooding over evil, you should not be in the business of trying to do karaoke with them. Get away from them.
Until tomorrow,
Gil Stieglitz