The Nicene Creed, which was certainly current around 381AD, is a corporate statement uniting Christians in a shared belief about God.
We believe in one God, the Father, the Almighty,
maker of heaven and earth, of all that is, seen and unseen.
In the ancient world it was common for people to believe in more than one God. Poseidon ruled the sea; Aphrodite was the goddess of fertility, love and beauty; Apollo was god of many things, including music, poetry, art, disease, medicine, light and knowledge, and so on. Early Christians were therefore liable to view this ‘Christian God’ as one amongst many others. Included in this array of so called ‘gods’ was the Roman Emperor. To deny his deity was unthinkable, and to say openly ‘Jesus is Lord’ rather than ‘Caesar is Lord’ was treason – it had political overtones. Hence the immediate emphasis on ‘We believe in one God,’ – when Christians took a stand on these words martyrdom could follow!
But notice this creed begins ‘We believe’ – it serves to unite us with all believers everywhere. Faith has moved on from being simply a matter of personal belief to being a corporate matter. Faith unites people around the world; we believe together and we belong together. Idiosyncratic stand-alone Christians are not part of God’s economy, unless such loneliness is totally unavoidable. Just as God is one – and we shall consider the Trinity tomorrow – the body of Christ, the Church is one. Our link with God, by faith, also links us with each other. Hence we can declare ‘We believe in one God’