In what way are nutmeg, cinnamon and cloves symbolic ingredients in mincemeat pies?

They are the ingredients of mincemeat pie. I don't know what you mean by "symbolic"?

http://whatscookingamerica.net/History/PieHistory/MincemeatPie.htm

Mincemeat pies are inexorably linked with Christmas for most of us, and that is purported to be because of the Crusades. The returning troops brought back the spices they had found and the trinity of Cinnamon, Cloves and Nutmeg were added to traditional mince pies. These were symbolic of the gifts the three wise men bestowed upon the infant Jesus and thus the bond between Mincemeat pies and the Christian celebration of Christmas was formed.

In honor of the birth of Christ, the mince pie was originally made in an oblong casings (coffin or cradle shaped). When the pie was baked it tended to fall a bit in the middle resulting in a cradle looking affair. It would then be decorate with an infant Jesus for serving. The baby was removed by the children and the pie was eaten in celebration. It was even thought to be lucky to eat one mince pie on each of the twelve days of Christmas.

hubpages.com/hub/Why-mincemeat-pies-are-meatless [no longer exists]
https://brewminate.com/the-history-of-humble-mince-pie-since-the-middle-ages/
https://www.smithsonianmag.com/smart-news/crusades-christmas-history-mincemeat-pies-180966981/