Here is another way of thinking about our movement through spacetime.

Take two cars having a race. The track is 100 miles long, and each car crosses the start doing exactly 100mph. The first car has all of it's motion in the direction of the track. The second car travels diagonally across the track, while still going 100mph. Therefore, it covers less distance down the track than the first car in the same amount of time, thereby losing the race.

The same can be said about our movement through spacetime. When we are moving in any direction (like car 2), we are covering less ground in time (car 1). So, the closer you get to the speed of light, the slower you travel through time.