2 Strikes, 3 Balls, and the bases are loaded. The pitcher throws the ball … and *thwack*! The hitter sends the ball flying deep into right field. The outfielder knows exactly where to go … and it’s caught.
A trajectory is the path that a moving object follows through space as a function of time. In this analogy, it was the space between where the ball was hit and the ball was caught. In the case of simple arcs, it’s easy to figure out where the object will stop.
I see Christianity in much the same light – Jesus was the Batter whose work to begin Christianity started with the early church. It flew through time and space, beyond the infield of history and into the outfield of the present. At some point, God will be the catcher, bringing the ball to completion. Until then, we’re the ball, flying somewhere along that arc.
Which is why I can’t stand the conservative takeover / resurgence going in in some mainstream Christian circles. It’s as if the ball has decided to turn around and head back for in the infield – the problem is that the ball doesn’t have any say in the matter but they’re going to try anyway.
The rest of us understand that we weren’t meant to always remain on the store’s shelf, or in the pitcher’s glove or flying toward the hitter’s bat, but we’re supposed to move forward – not knowing where we’ll end up, only knowing that we can’t go back to where we’ve been.