"Little Gidding," the last of the four poems in Eliot's Four Quartets, is, like the other three poems, concerned with time and the merging of the past, present, and future in the eternal now. One concern of the Four Quartets is the four elements: air, water, earth, and fire. The focus of "Little Gidding" is fire: the fire of Pentecost, in particular, that purifies and witnesses to the eternal presence of God. When we celebrate Pentecost, the coming of the Holy Spirit with tongues of fire, we celebrate the first Pentecost, and, on Pentecost Sunday repeat the same ritual of all past and future Pentecosts in an eternal now such that we "arrive where we began."
In the quote above, Eliot focuses on our seeking for answers, calling this seeking our "explorations." We will not stop "exploring" or trying to figure out the whys of life, be they the whys of the first Pentecost or the whys of the bombing of Britain. But as the imagery surrounding this quote suggests, the end of our exploring (questioning, seeking) brings us both back to paradise and forward to the New Jerusalem, which are one and the same: paradise is what we seek, what we can find if only we could see it, and where we will end up ("all shall be well"). But when we return there, which is already already here ("heard, half-heard, in the stillness ... here, now, always") we will finally understand it. As Eliot writes, what we seek in our explorations:
Is that which was the beginning [paradise];
At the source of the longest river
The voice of the hidden waterfall
And the children in the apple-tree
Not known, because not looked for
But heard, half-heard, in the stillness
Between two waves of the sea.
Quick now, here, now, always--
A condition of complete simplicity
(Costing not less than everything)
And all shall be well and
All manner of thing shall be well