The evidence from the Gospels culminates in the baptismal commission of Matthew 28:20. It is manifest from the narratives of the Evangelists that Christ only made the great truth known to the Twelve step by step.
First He taught them to recognize in Himself the Eternal Son of God. When His ministry was drawing to a close, He promised that the Father would send another Divine Person, the Holy Spirit, in His place. Finally after His resurrection, He revealed the doctrine in explicit terms, bidding them "go and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost" (Matthew 28:18). The force of this passage is decisive. That "the Father" and "the Son" are distinct Persons follows from the terms themselves, which are mutually exclusive. The mention of the Holy Spirit in the same series, the names being connected one with the other by the conjunctions "and . . . and" is evidence that we have here a Third Person co-ordinate with the Father and the Son, and excludes altogether the supposition that the Apostles understood the Holy Spirit not as a distinct Person, but as God viewed in His action on creatures.