A central theme in both yesterday’s (Shekaim 6) & today’s daf (Shekalim 7) is the status of מותר – (surplus) money that was set aside to be given for the half-shekel donation as well as for a variety of other Beit HaMikdash related functions and other charity needs, and fundamentally, the question posed by the Gemara is whether money that was intended for a particular purpose must still be used for that purpose, if more money than is necessary has been collected for that purpose.
Interestingly, rather than the Gemara giving a general rule for all cases, each case is treated differently. For example, מותר for shekalim is considered to be chulin (non-sanctified), while מותר for some sacrificial offerings (eg. chatot & ashamot) are assigned as voluntary communal offerings (נדבות), and מותר for other offerings (eg. mincha offering) are used for those particular offerings.
On first glance, this may seem surprising, for surely the initial intention of the giver should be the exclusiver decider in terms of how the money which they donated should be used.
However, from the different answers given to the different cases discussed in our Gemara, it seems that the channelling of money for Temple use was determined not only by individual intention, but also, by pragmatic need, such that if money was unnecessary for one fund, and there was evident need for its use elsewhere, then it could be used for another.
Finally, towards the end of Shekalim 7b the Gemara cites Mishlei 21:3: ‘performing charity and doing what is just is more acceptable to God than sacrifice’ – which reminds us that the way that money is used should always be a sacred concern, and that if excess money is discovered, then it should be used for just and appropriate causes.