The soul, being eternal, is not bounded by time components such as past and future. It is that part of us that cannot die, is not born, and is not bound by the physical properties of time and space. It is therefore outside of the laws of cause and effect. Cause and effect imply time and space: You throw the ball. In a split second the ball flies through the air to another space. Newtonian physics do not apply to the soul.
Therefore, to understand who you are as an eternal soul, ideas such as purpose and usefulness, practicality and future payoffs, are not relevant. If you put the question another way, “What is our true purpose?,” I would reply, “It is to get acquainted with who we really are as our souls.” But the soul itself, like life itself on the highest level of contemplation (beyond eating, procreating, and grabbing a bunch of toys before we die), is gloriously purpose free in its grandeur and magnificence.