Beyond all temporary circumstances that may permit, explain and favour some Christians’ denial of the Holy Trinity, the real roots of it can be found in the paradox, as it seems to be, of a God who is simultaneously One and Three. Common sense can not understand this, nor can it understand why the members of the deity should be only three and not four or five, or two, etc.
The whole problem is caused when we are not in an existential search for God, but in a rational attempt to comprehend/invent a theory. How do I know that? Because, if a person is in a real search for Him, God is obliged to help this person and to reveal Himself in this person. The same happens in the secondary dimension, in cultural traditions.
It is not a coincidence that the New Testament is written in Greek, Christianity was adopted by Greeks, and the Church of the first centuries has a clearly Greek identity (Cf. Greek Orthodoxy – From Apostolic Times to the Present Day). After the ancient Greeks’ unbelievable attempt to get close to Him, God was obliged to respond. Christianity is this response. The same happens in the primary, properly personal, level, i.e. with each person.
So-called “pure monotheists”, whether they belong to the Judaic, the Muslim, or any tradition of such a kind, they are in reality not monotheists but atheists. Abolish the Trinity, and you also abolish Oneness. After such an abolishment, the One that is worshipped is not the God, but the idea of a creature.
Only a creature can be one in the sense of the Judaic or the Muslim oneness – God is One only in the Trinity. But all of these things are closed in a darkness, away from impious people. Therefore, no matter how many essays are written, how many wise and holy men speak to us as they have, the Fathers of Christianity, no matter how many and how greatly they speak, we must not expect that “pure monotheists” will be persuaded, because this is essentially not a matter of arguments and persuasion.