What is the meaning of [Harp not for ever on the same string]

Don’t keep on talking about the same thing or bringing up the same subject.
Literally ‘to harp’ means to play the harp; figuratively ‘to harp on’ is to
dwell tediously on a matter.

##### See also:

* Don’t take your harp to the party
* It is useless to flog a dead horse
* Not good is it to harp on the frayed string