It seems that in reality the doctrine of the Trinity is that which is necessary to make sense of the New Testament statements regarding God the Father, the Son, and the Holy Spirit, and their relations to each other and to men, rather than that which is openly taught and advocated by the New Testament.
We may break the doctrine down into four parts for study in the New Testament. (1) The first point in the doctrine is that of unity, that there is one and only one true God. (2) The second is that there is a person called the Father, who is also called God. (3) Third, there is a person called the Son, or Christ, who is called God. (4) Fourth, there is a person called the Holy Spirit who is called God. It need only be added that the first point is, as it were, an umbrella over the other three, so that we will not fall into the erroneous view of the three names standing merely for different relations of one person to the creation. That is, the three persons of the Trinity are really three persons, and really one God.
— Calvin Beisner, from God in Three Persons, p. 26