The past is gone, a gift used up and set aside.
The present is the only moment that is real, that matters, because it is the gift that we have Now.
And yet, the present so quickly and so easily becomes the past, used up, lost, unavailable, except to some degree in memory.
So, we only have a moment in which to live the present moment before it becomes the past, before it is lost to us.
In the present, we can know God's will: it IS this moment, with whatever it contains. It IS what God has given us.
So: work, joy, trial, silence, noise, love, hatred, whatever the moment consists of, is that which God has given me.
We cannot waste this gift by longing for the future. It may never come. Or mourning the past. We cannot change it. We may learn from the past, but not if we dwell on it to such an excessive degree that the present passes unnoticed.
We must not squander the gift of the present through impatience or reluctance or sin.
We must intend to live each moment as faithfully and as fruitfully as possible. This is primarily by accepting it and living it for love of the Giver, for love of God.
And nothing we do can be truly faithful or fruitful if it is done for any reason that excepts the love of God.
Even if we are forced, for instance, by the circumstances of the present moment, to not perform a good - for instance we must miss Mass in order to care for a sick person, the present moment becomes subjectively more valuable in God's eyes if we live is with patient acceptance for love of God.
In fact, to neglect our sick one in order to attend Mass could be subjectively displeasing to God, because caring for the sick was our duty, neglected to attend Mass, manifesting a preference of our will over God's. It could be said that most of the evil in the world arises from a "contempt" for the present moment, for the circumstances in which we find ourselves, even those circumstances that may arise as a consequence for our previous bad choices.