A currency serves two purposes:
1) value exchange
2) value storage
The idea that value can be stored is *mostly a myth. An ideal currency under the right conditions can appear as if it is storing value and that's good enough most of the time so it's not too much of a stretch to behave as if it really is "storing value".1) value exchange
2) value storage
But ultimately value is the willingness of another person to give you something else for what you have. Willingness is not storable so the capability to store value can only be emulated.
*You can store tangible goods and they will keep some inherent utility but that's a minor part of the economy.