'Fast' in the Bible

‘I know where you dwell, [a place] where Satan sits enthroned. Yet you are holding fast to My name, and you did not deny My faith even in the days of Antipas, My witness, My faithful one, who was killed (martyred) among you, where Satan dwells.

except to hold tightly to what you have until I come.

Because you have kept the word of My endurance [My command to persevere], I will keep you [safe] from the hour of trial, that hour which is about to come on the whole [inhabited] world, to test those who live on the earth.

I am coming quickly. Hold tight what you have, so that no one will take your crown [by leading you to renounce the faith].