There is no need to be worried by facetious people who try to make the Christian hope of “Heaven” ridiculous by saying they do not want “to spend eternity playing harps.” The answer to such people is that if they cannot understand books written for grown-ups, they should not talk about them. All the scriptural imagery (harps, crowns, gold, etc.) is, of course, a merely symbolical attempt to express the inexpressible.
Musical instruments are mentioned because for many people (not all) music is the thing known in the present life which most strongly suggests ecstasy and infinity.
Crowns are mentioned to suggest the fact that those who are united with God in eternity share His splendour and power and joy.
Gold is mentioned to suggest the timelessness of Heaven (gold does not rust) and the preciousness of it.
People who take the symbols literally might as well think that when Christ told us to be like doves, He meant that we were to lay eggs.
Mere Christianity, book 3, chapter 10 (on “Hope”)
HT: Jack Collins