Summary: The preexistence of God and the plurality of His Persons. The order of Creation, and the presence of God's wisdom.
"In the beginning God" implies that God existed before the beginning of time. No mere thing existed before the beginning, but only God. There is no duality, no struggle between equal forces of good and evil: just God.
Yet we see God in community with Himself. When God creates man, He says let "us" make man in "our" image, after "our" likeness.
We see Him as the Creator, making all things of nothing. We see Him as the Spirit moving across the face of the deep. And when He speaks the word which sets Creation in motion, we have a hint of the one whom we see more clearly in the New Testament: Jesus (John 1:1-3).
The rhythm of Creation is nicely balanced in this poem. And whilst Genesis 1 is not a scientific thesis, it would not be true to say that it is unscientific. The order of events is not in dispute.
Light is created in the first day, prior to the luminaries which we see in the sky. It is only in the fourth day that the sun, moon and stars appear.
In the second day the vapour above is separated from the seas beneath. On the fifth day both watery realms are teeming with life.
Dry land appears on the third day, giving our planet its name, Earth. Grass, herbs and trees appear, each bearing their own seed.
On the sixth day animal life is created, each after their kind (i.e. without cross-species evolution.) Finally man is created in the image of God.
We are told in this account that when God made man, "male and female created He them." Our communal existence echoes the community within the Godhead. We have a rational soul, and the in-breathed spirit of God.
Each of the days of Creation is punctuated with "the evening and the morning." Yet when we come to the seventh day, the sanctified day of rest from God's original labours, the formula is absent.
Proverbs 8:22-31 provides a fitting commentary on this chapter from the point of view of God's wisdom.