The present is the point at which time touches eternity (C.S. Lewis said that,not me). This seems to me to be an admonition against both laziness and worrying. We cannot change the the past obviously and the only thing we can really do about the future is pray. And we should pray-guess when-today!
The present moment is the only time we are given deciding power (and that's a relief-think of who would do what with their One Rings) over. We do have choices and freedom,but only if our god is God and not worries and past shadows and ambitions and lusts and fears.
Go live today my friends! And since I just have to end with a Gandalf quote,
"All we have to decide is what to do with the time that is given to us."
P.S. "Happy work is best done by the man who takes his long-term plans somewhat lightly and works from moment to moment 'as to the Lord'. It is our daily bread that we encouraged to ask for. The present is the only time in which any duty can be done or any grace received." ~Lewis,The Weight of Glory