Did the early church have a simple concept of the Trinity?

The oldest New Testament manuscript discovered is from the Gospel of Mark and dated at before Mark’s martyrdom in AD 68. This is within 35 years of the resurrection, within the lifetime (one generation) of those who knew the truth about Jesus.

In the Gospel of Mark 1:2-4 we read: 2 Just as it is written in the prophet Isaiah, “Behold, I am sending my messenger before your face, who will prepare your way, 3 the voice of one shouting in the wilderness, ‘Prepare the way of the Lord, make straight his paths!’” 4 John was there baptizing in the wilderness, proclaiming a baptism of repentance for the forgiveness of sins.

Mark starts by quoting the prophet Isaiah which is repeated by the prophet Malachi.

Isa 40:3 A voice is calling in the wilderness, “Clear the way of Yahweh! Make a highway smooth in the desert for our God!

Mal 3:1 Look! I am going to send my messenger, and he will prepare the way. And the Lord whom you are seeking will come suddenly to his temple.

Clearly Yahweh, God Himself, is coming and is headed to His Temple. It is understood that John the Baptist is the messenger calling in the wilderness. And who shows up heading for the Temple? Jesus. Enough said.