Time is the measure of duration. Time began when " In the beginning God created heaven and earth” and it will terminate with the renovation of the world on the Last Day. In regard to man's existence time may be considered in three ways: (1) in the strict sense, as the measure of man's earthly pilgrimage; (2) in a wide sense, as the span of human life; (3) and as man's probation period for eternity. As a measure of duration time is a momentary quality of life that is unceasing in its progress, passes quickly, and never returns.
Strictly speaking only the present moment is time. It connects the eternity of the past with the eternity to come. The activity of the present ceases as soon as it is recorded in the history of the past. The mistakes of the past may be remedied in the present, but vain schemes about the future are a double loss, because they squander the present and build on an uncertain future. Whether man seizes the present opportunity, or permits it to glide idly by, the stream of time moves on unceasingly. As the present moment alone is his, it would be the height of folly to indulge in useless regrets about the past or entertain visionary plans about the future.
As the span of human life, time is like a rainbow with one end resting in the cradle of the obscure past, and the other projecting into the more uncertain grave of the future. Man's span of life is like a rainbow (1) because the duration of both is brief and uncertain; (2) because both develop their luster in the present; (3) because both may be obscured and destroyed by any trivial cause.