Basically, you have made the recipient of your bag/parcel an importer, and it will be treated as a commercial shipment. Whoever it is sent to may need to pay any import duties, excise if applicable, and other relevant taxes (such as VAT). While it is sometimes a difficult notion to grasp when dealing with things we think of as our personal possessions, most countries have a similar regime. If the shipment contains restricted products, they may be confiscated or held until other clearance requirements are met.
In contrast, the items that you bring with you as personal baggage when you arrive are considered personal possessions, not imports. The text (in English) from the Spanish Agencia Tributaria states in part:
All goods contained in traveller's personal luggage entering mainland Spain and the Balearic Islands from third countries, the Canary Islands, Ceuta or Melilla will be exempt from import duties as long as they are exempt from VAT and Excise Duties, subject to the fulfilment of certain conditions. To the effects of this Law, goods carried by travellers will not be considered a commercial shipment as long as they are an occasional purchase, for the traveller’s personal use, that of their family, or to be offered as gifts, or as long as their nature and number does not lead to conclude they are aimed at a commercial activity.
Unless you can convince the Agencia Tributaria that these are personal possessions rather than a commercial import, you might be better off paying the import duties etc to have the bag released. It will certainly be far less expensive than purchasing a completely new set of gear.