Why does the narrator in "A Psalm of life" say we should not trust the future? What does he suggest?

People tend to trust and depend on the future for many things because it appears to be promising and pleasant. The narrator in “A psalm of life” advises people not to look back or hold back the past and even not depend on the future. What one has is the present and should make the most of it. People believe in the future to be better than the present keeping too much faith in God. People these days are actually never satisfied with what they already own and always tend to find a source of happiness in whatever they don’t have. Future is uncertain and once the present is gone there is no way one can bring it back. The only thing a person does is complain and lament about the situation. The primary motive of anyone should be to build the present. This poem too emphasizes on the importance and need to act and live in the present. With a strong heart filled with determination and a little trust in God, one can easily sail through life.