“For the Spirit Within Us”
Everything we do is for the spirit within us – and for others (as is everything done by others to us). The more we are aware of this, the more the act may be called altruistic.
The reason, if such there be, for knowing the spirit within us is that we can dedicate our lives to being altruistic.
So why are we not told?
Perhaps the Sages – only the Sages – do know, and live accordingly.