At first read this is simply a reference to the one hundred twenty-year delay between God’s promise to destroy the earth and his carrying out the plan. Yet there is a richer element to this clause. God determined to save Noah (Genesis 6:8, Genesis 6:14, Genesis 6:18), and was pleased to use the ark as his means of saving. The saving was from the water, and via the water from the suffering and abuse that Noah received from his apostate neighbours. So the clause underscores God’s impatient forbearance for the completion of the ark as the means of saving Noah from his tormentors. That God would be impatient to save is encouragement for Peter’s readers as they suffer; God is impatiently patient
as he prepares their deliverance. No doubt Peter’s readers were not so patient as they awaited their deliverance from unjust suffering.
20 because they formerly did not obey, when God’s patience waited in the days of Noah, while the ark was being prepared, in which a few, that is, eight persons, were brought safely through water.