This essay introduces some fundamental concepts which depend closely on each other.
Ironically, I start a series of essays leading towards a description of eternity, by introducing time.
Time, as observed from the inside of it, is an ordered sequence through which the observer progresses. It may be observed as a continuum or as a sequence of points. Unless stated otherwise, I will use terms such as a point in time as being valid whether or not we regard time as a continuum in that context.
An observer is always at only one point in time, and then moves to a later point. Having been at a point, the observer can never return to that point; the progression of points is monotonic. The observer's presense at each point in time is for an infinitisimal duration.
An observer may view time as being partioned into a series of intervals. An interval contains a series of consecutive points in time; all points between the points in the interval are also in the interval. Time being a sequence of points, the division of time is a scalar quantity.
An observer may observe two or more time intervals to be of the same length. This length may for convenience be measured in terms of some physical phenomenon. Having chosen a unit interval length, the observer will measure an interval of time as a scalar multiplier of the unit interval length.
One of the most significant things about time is that it goes in one direction, along a single line. You cannot go back, nor can you change what has been. This has moral and theological implications; deeds cannot be undone, and not all events can be compensated for. Bad deeds cannot be undone; justice must take this into account, and hence mercy is necessary, and repentance is not able to undo actions.
Some events mark transitions from one state to another; indeed, it could be said that all do. One such transition marker is bodily death, generally taken to be irreversible although exceptions have been recorded... but these exceptions are not reversals in time, but a restoration of life, a further transformation.
However, they may be reversals in the sequence of states; and so it may be said that by his resurrection, Christ reversed the process of death; however, it may also be said that he did not reverse it but went beyond it.