To impress upon you what I mean, I'm going to present you with two different models of God in a Mormon context, one light, and one not so light.
The Heavy God lives on a planet called Kolob, located at the center of the universe. He can only dwell at one place at one time, and so he must travel between this planet and Earth fairly instantaneously. This naturally means that Einstein's Theory of Relativity is incorrect. God also has a physical body of flesh and bone, free of all imperfection and blemish. Except the prints in Christ's hands, of course - He needs those. He also lacks any blood, for blood is the mark of a mortal body. Further, the Heavy God hears our prayers by means of a sort of divine telepathy, and can manage all prayers at once because his brain uses the 90% left unused in ours.
The Light God is an exalted man, and by following Him we can learn to be better people. When we pray He answers us and fills us with the Spirit, and He loves us unconditionally. Christ sacrificed Himself for us, and we can cast all of our sorrows and pains upon His back if we turn to Him. He is love, and we experience Him whenever we show love. God is our cosmic parent, and loves us and cares for us as any loving father would.
See the difference? One of them is full to the brim with the Spirit, and one of them lacks any spirituality whatsoever. One of them embraces the truths of the Gospel wholeheartedly, and the other seems like it wants to be a facet of science more than one of spirituality. But there is a common feature here - the former tries to combine spiritual beliefs with truths found outside of spirituality, and thus ruins the emotional value of the Gospel. On the other hand, the latter sees only the meaning within the Gospel, keeping outside truths in their own separate compartment. Or if I might phrase it differently - one of them values objective truth, and one of them values meaning.
In my life, I experience the peace of the Gospel only when I consider the meaning of spiritual principles, doctrines, and stories. If I start to wonder how these things fit in a cold, rigid external world, the Gospel loses all of its inherent warmth, and its meaning goes away.
You see, this meaningful God is light. When we see Him as a loving Father and not as a super-powerful alien, He can fit through the narrow door of our Spirit and fill our thoughts much more readily than something heavy. Heaviness means friction. The Heavy God must squeeze through this door to come in at all, but this does not really ever happen. The light God is also a piece of art. We think of this type of deity in much the same way in which we think of a painting, a piece of music, or a movie - full of beauty and warmth. And yet, this God is much more than a work of art, for he is a work of art come to life. He has leapt from the canvas, and become real.
If I could preach one truth loudly from the rooftops, it would be this: do not pursue facts, but seek after meaning! If you only look for the objective, you will only find the objective. And because meaning must come subjectively, this life of this seeker after truth will lack any warmth, color, or beauty. But if you seek after love, beauty, compassion, and emotion, you will find a truth much more powerful than anything seen through the lens of a telescope or a microscope.
As a closing note, it is incredibly important that the D&C describes God as being seen through "the light of our understanding". For if we seek for God using the light of day, we will not find Him. But if we seek him using this more divine illumination, we will see that He has never left our side.