The verb mellō expresses imminence, intention, or certainty of future action — 'to be about to do something,' 'to intend to act,' or 'to be destined.' It is frequently used with an infinitive: mellei + infinitive = 'he is about to / is going to [verb].' In eschatological contexts it carries the weight of divine inevitability: what is mellōn (coming, future) is what God has purposed and nothing can stop.
Romans 8:18 is one of the great comfort texts built on mellō: 'I consider that our present sufferings are not worth comparing with the glory that will be revealed [mellousēs] in us.' The coming glory is not merely possible but imminent in the divine timetable — already pressing against the present age. Hebrews uses mellō to describe Christ as the inaugurator of the 'coming age' and its blessings (Heb 1:14; 2:5; 6:5). In Matthew 2:13, the angel warns Joseph: 'Herod is about to [mellei] search for the child to kill him' — mellō as warning of imminent danger. Acts 26:22 summarizes Paul's message as what 'the prophets and Moses said would happen [mellonton]' — the whole OT as anticipation of the Christ event that was always on its way.