How likely is it for a person, who has never heard of the concept of the Trinity before, to discover Trinitarianism, independently, on their own, by just reading the Bible? Are there any published testimonies from Christians who became Trinitarians in this way?
For the purposes of this question, I'm assuming the definition of the Trinity proposed by the Athanasian Creed:
Whosoever will be saved, before all things it is necessary that he hold the catholic faith. Which faith unless every one do keep whole and undefiled, without doubt he shall perish everlastingly. And the catholic faith is this: that we worship one God in Trinity, and Trinity in Unity; neither confounding the Persons, nor dividing the Essence. For there is one Person of the Father; another of the Son; and another of the Holy Ghost. But the Godhead of the Father, of the Son, and of the Holy Ghost, is all one; the Glory equal, the Majesty coeternal. Such as the Father is; such is the Son; and such is the Holy Ghost. The Father uncreated; the Son uncreated; and the Holy Ghost uncreated. The Father unlimited; the Son unlimited; and the Holy Ghost unlimited. The Father eternal; the Son eternal; and the Holy Ghost eternal. And yet they are not three eternals; but one eternal. As also there are not three uncreated; nor three infinites, but one uncreated; and one infinite. So likewise the Father is Almighty; the Son Almighty; and the Holy Ghost Almighty. And yet they are not three Almighties; but one Almighty. So the Father is God; the Son is God; and the Holy Ghost is God. And yet they are not three Gods; but one God. [...]
Note: Why am I asking this question? Because it would be interesting to know to what extent the doctrine of the Trinity can be inferred from Scripture alone, without any significant cultural bias influencing the individual's private interpretation of the text in favor of a particular doctrine. If unbiased readers consistently fail to become Trinitarians, that should be food for thought. On the contrary, if those testimonies actually exist, that should be food for thought as well. So, whatever the answer, I personally find this question quite interesting.