What is there to say about the belief of the early Christians, who were not familiar with the formulation of the dogma of the Holy Trinity. Was their belief recognised as legitimate?
Answer: One has to differentiate between the theological formulations, which have given rise to the expression of Christian faith over the course of time, and the content of the Christian faith.
At the beginning of the Christian faith is the fact that people had discovered, in a very „revolutionary” way for them that in Jesus of Nazareth and in the power of his spirit, God Himself had come down to His people. Through them God had not shared something of Himself with them but literally Himself. In Jesus Christ, God comes into the world personally. Our world is now also His world; He assumes our destiny and in doing so creates the most intimate cohabitation between Himself and humanity. That means, however: In Jesus Christ and – in other ways – in the Holy Spirit sent by him we meet emissaries that only point to God (just as prophets or holy people also refer to God) behind whom, however, the deity remains elusive from humanity in hidden, unending transcendence for ever. Now, in the Christ event God brings Himself into the game. Whoever has dealings with Jesus, His word, His bearing, His suffering, whoever experiences the spirit in themselves and working around them is dealing with God personally. If it were not so, Jesus, who comes as Gods final valid word and as the unsurpassable embodiment of divine love, would stand in contradiction to Himself. He would then not be the final intervention between God and humanity which, however, He claims for Himself: “Whoever has seen me has seen the Father” (Jn 14:9). And also the Holy Spirit, which fills Jesus, led us to the reality of Christ after His homecoming to the Father and opened up the direct access to the Father. He would leave us in the realm of the creatural, if He were not God Himself. See also Book 5, III, 7