1 Peter 1:2
1 Peter 1:22according to the foreknowledge of God the Father and sanctified by the Spirit for obedience to Jesus Christ and sprinkling by His blood: Grace and peace be yours in abundance.
Read as describing Jehovah's foreknowledge, the operation of his active force in setting people apart, and the value of Christ's ransom — three elements of one arrangement rather than three persons. The Watchtower would note that the verse distinguishes the Father from Jesus, which it takes as evidence against the Trinity.
Nobody claims a single verse proves the Trinity, and it is worth saying so before using this one. The doctrine is the summary of three things Scripture teaches separately — that there is one God, that Father, Son and Spirit are each called God, and that they are personally distinct. What this verse contributes is the last of those, in a form Peter clearly did not invent for the occasion. Chosen according to the foreknowledge of God the Father, sanctified by the spirit, for obedience to Jesus Christ and sprinkling with his blood. Three named parties, each with a distinct role, in a greeting written without argument or defence. That triadic shape recurs where nobody is arguing about it: with one name for three; with grace, love and fellowship; with the same spirit, the same Lord, the same God. The point is that the pattern predates any council. Christians did not deduce the Trinity from philosophy and read it back in; they found these three named together as a matter of course, and eventually had to say why. Compare , .