We also don't "understand" what drives the occurrence of gravity. We live under its power every day, in and out, it is one of the most fundamental forces acting on all of our lives, yet we can't explain it. Where does it come from? Why is mass attracted to mass? Does gravity necessitate a God to have enacted it? If so, why?
From the same perspective, we don't understand "life". So what? "Life" could be as immutable a circumstance as gravity within our universe. Why not? Even non-life strives to arrive at the most "beneficial" configurations. Elements seeks out other elements to form more stable and lasting bonds, even abandoning current relationships within less stable molecules - without anything needing to intercede. A vacuum, when presented with matter, is filled with that matter as quickly as possible, and heat reacts in the same way via entropy. Balances, and effects that range the gamut of mutual "benefit" abound in the universe. Why couldn't life simply be another of those strivings? Always at the ready when conditions are right.