I always feel like the feast of the Ascension is about how, in our existential experience of faith and especially in prayer, there is always a tension between our senses of the presence and absence of God.
God, in a very mysterious way, is both presence and absence. His Presence, beneath, within, around (pick your metaphor!) everything--we know this Presence as the Spirit Who is the Gift of both Jesus and the Father.
On the other hand, often what we feel is the absence of God: "Men of Galilee, why are you looking up into the sky?" This sense of absence can make us desire the Mystery more, or it can be discouraging. We feel it every time we try to utter anything about God; as soon as we rejoice in some insight, we notice that, well, it's not quite what we had hoped to say.
It's easy to get at this spiritual tension with the little kids with whom I do a children's liturgy of the Word on Sundays. I sometimes ask them if anyone has ever seen God. In perfect agreement with the doctrine of the letters of John, they say, no, nobody has ever seen God. But then I ask them where God is. Invariably I get the same three suggestions, always in the same order. First, God is in heaven. Second, God is in our heart. Third, God is everywhere.
Now I don't push them into the obvious and very mysterious question: How is that Someone is both everywhere and in each individual heart, and yet we easily admit that nobody has seen Him or is comfortable making any claims about Who He Is? I know they feel the Mystery on some level, and I wouldn't want to ruin that with words.