I like how C.S. Lewis describes living totally in the present, that when the work of today is to meditate and learn from the past or schedule an appointment for the future, then you are not dwelling in the past or the future, but doing the work of the present, which sometimes is about the past or the future.
But when you are brooding over past injuries or stewing about future worries, then you are not in the present, which is the only place we can connect with God. The past is done; the future may never come. Only in the exact NOW can we meet with the One who matters most and whose timing can be totally trusted to be for our benefit.