Riddle: The Enigma of Time

In the depths of the night, or in the light of the day,
It's always present, it never goes away,
Sometimes it drags, sometimes it flies,
It's never ending, it never dies.

It is a thief, that steals moments untold,
And a friend, that makes memories unfold,
It's a teacher, that shows us the way,
It's a judge, that makes us pay.

It's the fire that burns, and the ice that cools,
It's the laughter, the tears, and the passing of fools,
It's the rhythm of life, and the beat of the heart,
It's the mystery that we cannot impart.

It can heal the wounds, or tear them apart,
It can mend bridges, or break them apart,
It's the magic that makes life so sweet,
It's the curse that makes it bittersweet.

So, tell me, what is this thing I speak of,
That's so precious, so rare, so full of love?