“But this fact” — the fact that G-d’s presence suffuses all of existence, and that He interacts with us moment by moment, wherever and whomever we are — “only touches you personally if you constantly reflect upon it and observe it”, Ramchal remarks. That’s to say, it will only touch your heart if you take it to heart, again and again.
For “this sort of thing is beyond our ordinary perceptions, and the mind can only grasp it after much meditation and contemplation”, which isn’t hard to understand given that G-d Himself can’t be seen and His ways often can’t be discerned (both inherently and because we simply don’t make the effort to try).
“Even if it had made an impression” once you’ve made the effort, that impression “will (still and all) be easily lost if you don’t constantly work at it” since it’s so subtle, so demanding, and so astonishing. So you’d need to be diligent as well as determined to catch hold of G-d’s presence in this world as it rounds each corner and settles in every nook to escape your gaze.
Beware, though, for “just as a lot of contemplation is the only way to attain constant fear of heaven, diversion of attention … or lack of concentration is the way to lose it”, as each time you take your mind off of G-d’s presence, you “distract (yourself) from the state of constant fear of heaven”. That is, just as we’d need to ruminate and again about precious moments we’ve shared with loved ones, perhaps on vacation, at family reunions, on special occasions, and the like, in order to deepen the love and connection, we’d certainly need to do as much to solidify our encounters with G-d’s presence in the world.