The poem
In the beginning was the three-pointed star, One smile of light across the empty face, One bough of bone across the rooting air, The substance forked that marrowed the first sun, And, burning ciphers on the round of space, Heaven and hell mixed as they spun.
In the beginning was the pale signature, Three-syllabled and starry as the smile, And after came the imprints on the water, Stamp of the minted face upon the moon; The blood that touched the crosstree and the grail Touched the first cloud and left a sign.
In the beginning was the mounting fire That set alight the weathers from a spark, A three-eyed, red-eyed spark, blunt as a flower, Life rose and spouted from the rolling seas, Burst in the roots, pumped from the earth and rock The secret oils that drive the grass.
In the beginning was the word, the word That from the solid bases of the light Abstracted all the letters of the void; And from the cloudy bases of the breath The word flowed up, translating to the heart First characters of birth and death.
In the beginning was the secret brain. The brain was celled and soldered in the thought Before the pitch was forking to a sun; Before the veins were shaking in their sieve, Blood shot and scattered to the winds of light The ribbed original of love.

When I first started getting into poetry I rented a tape of Dylan Thomas reading his poems and I just didn't "get it" for some reason. I guess I wasn't able to get past it's complexity to connect with it or something... But now I love reading him, especially this one, its so rich and profound and seems to speak to something terrifying yet incredibly beautiful. I can imagine him reading each consecutive stanza louder than the previous one, building tension. it seems like its that type of poem.
It's easy to get lost in the beauty of Thomas' words. One is tempted to read his work and recite verses out loud, just to be seduced by their musicality and the metaphysical conjurings they elicit- I've done it many times myself. This poem is indeed beautiful, but make no mistake, it is not an unequivocal celebration of creation. Thomas couches the appearance of man, his firs traces, in soaring images and metaphors of cosmic and Biblical roiling but if you read carefully you'll catch (particularly in the last stanza) a subtle tone of ruefulness or reproach.
There has much nonsense been written about his poetry the vast majority emanating from the USA. They seem obsessed by the search for "meaning" Dylan Thomas's poetry is not about meaning but about sound. It is closer to music than prose. Do not look for meaning! Just listen to the sound.