Give us thyself, that we may see...

Give us thyself that we may see
The Father and the Son by thee.

So John Dryden interprets part of the great 9th century hymn to the Holy Spirit, Veni Creator Spiritus - accurately capturing at least part of the concern of the original.  We seek the Spirit, so that by the Spirit we might know the Father and the Son (and, in the slightly more Trinitarian formula of the original Latin composition, might know the Spirit himself also).

The doctrine of the Holy Spirit plays a vital role in the doctrine of revelation.  Put it in the context of the whole Trinity.  The Father is the unseen, and the Son is the visible image of the invisible God.  The ancient argument for the deity of Christ revolved around this: if the Son is not God, then God is not revealed.  Nothing less than God could truly reveal God to us.  But granted the deity of the Son: how does it come about that a human being, who is not God, can have God revealed to them?  If it is true that only God can reveal God, is it not also true that only God can see God?  In other words, even granted the true revelation of God in the person of Christ, we human beings have absolutely no inherent capacity to receive this revelation.

Without God (the Spirit) working in us, we cannot see God (the Son) revealing to us the being and person of God (the Father).  And so we pray, Come, Creator Spirit!