The Greek demonstrative pronoun ekeinos means 'that one' — pointing to something previously introduced or at a distance from the speaker. It is the emphatic demonstrative, contrasting with houtos ('this one' nearby). In theological discourse, it often points back to an antecedent of great significance: 'that day,' 'that word,' or most profoundly, 'that one' meaning Christ or the Spirit.
Ekeinos is used with remarkable theological precision in John's Gospel and letters. John 1:8 describes John the Baptist: 'He himself was not the light; he came only as a witness to the light. That one was the true light.' 1 John 2:6 commands walking 'as that one walked' — a reference to Christ without naming him, conveying deep reverence. The Spirit is 'the Helper, that one' (ekeinos, John 16:8,13-14) — the masculine pronoun used even though 'Spirit' (pneuma) is neuter, signaling the Spirit's personhood. Ekeinos thus becomes a vehicle for Trinitarian theology.