He said. Probably some time after Mark 16:14, on the eve of the Ascension.
world = kosmos. App-129.
preach. proclaim. Greek. kerusso. App-121.
the gospel. the glad tidings.
every creature. all the creation. Put by Figure of speech Snec doche (of Genus), App-6, for all mankind.
Fulfilled during "that generation". See Colossians 1:6; Colossians 1:23.