God, who at sundry times and in divers manners spoke in time past to the fathers by the prophets,
The "word of His power" is the word that expresses and conveys His power. He "upholds all things," i.e., sustains the organic body of the universe in all its applications, as one who made the world (ver. 2). In Colossians 1:17 the idea is slightly different; there the Son is the element in which the universe holds together, here He consciously sustains it.
(A. B. Davidson, LL. D.)
Parallel VersesKJV: God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets,