When we do, we alleviate ourselves to the exalted human standard Allah wants us to achieve. We believe in Him as a result of an intellectual choice. Whether good actions done by unbelievers are of any great value or not is something with which we should not concern ourselves over much. As human beings, we are not in a position to judge others. We accept the criterion Allah has told us, through His last Messenger, that applies to us.
Actions acquire their value through faith.
What He does with His servants on the day of judgement is His own concern. What we know is that He does not deal unjustly with anyone. It leaves out nothing, be it small or great, but takes everything into account. And they will find all that they ever did facing them now, and will know that your Lord does not wrong anyone.