“But I tell you of a truth, there be some standing here, which shall not taste of death, till they see the kingdom of God.”
Truly I tell you, some who are standing here will not taste death before they see the kingdom of God — the timing saying addresses the imminence of the kingdom's visible manifestation: some present will see it before they die. The transfiguration (six days later) is one fulfillment; the resurrection and Pentecost are others; the spread of the kingdom through the Roman Empire within a generation is another.