One of the earliest creeds created by Christians (besides “Jesus is Lord”) is the Apostles’ Creed:
1. I believe in God, the Father almighty, creator of heaven and earth.
2. I believe in Jesus Christ, his only Son, our Lord.
3. He was conceived by the power of the Holy Spirit and born of the Virgin Mary.
4. He suffered under Pontius Pilate, was crucified, died, and was buried.
5. He descended into hell. On the third day he rose again.
6. He ascended into heaven and is seated at the right hand of the Father.
7. He will come again to judge the living and the dead.
8. I believe in the Holy Spirit,
9. the holy catholic Church, the communion of saints,
10. the forgiveness of sins,
11. the resurrection of the body,
12. and life everlasting.
Apparently, the earliest (extant) written version of the creed comes from around 390 AD. However, many believe that this creed is much older, perhaps dating to the second century.
Thus, this statement was written and used by many early Christians at a time when the church was discussing and arguing about many different things. Now, one of those arguments concerned the nature of Jesus Christ and his relationship with God, which is covered by the creed.
But, there were other discussions, arguments, and disagreements as well: baptism, communion (eucharist), bishops/pastors/elders/deacons/etc., and on and on. However, these items did not find their way into the earliest of creeds.
Why do you the earliest creeds did not include some of these items? Why do you think they only focused on the few key aspects listed above? Why do you think modern day creeds and confessions go into much more detail?