The ark was finished, and it was time for the vessel to be put into use. When God commanded Noah to build the ark 120 years ago, it must have been a relatively abstract idea to Noah. Noah had simply been given the dimensions of the ark— he had been given the blueprint of the ark. And just as seeing a house is much different than seeing the blueprint of a house, so when Noah finally saw the completed ark, it must have been much more real to him than when he first received its “blueprint”.
At last, the expected words from God came: Enter the ark. When Noah finally heard these words, perhaps he thought back 120 years ago to the moment when he first received the “blueprint” for the ark. Perhaps he thought back to the moment when the construction of the ark seemed to be an impossible task.
But over those 120 years, the ark had gradually come together. Over those 120 years, Noah had, so to speak, worked while it was day, because the night was quickly approaching when he would no longer be able to work (John 9:4).
What at first might have appeared to be impossible to construct, was about to be put into practical use. God said to Noah: Enter the ark, you and all your household. And why was Noah and his household entering the ark? Why was it that Noah and his household would be saved, but all others would perish?
The Time Comes to Enter the Ark (Part 3) - Genesis 7:1
Summary of Genesis 6
Noah's Obedience - Genesis 6:22
State Of The World (2469 BC): 120 Years Before The Flood - Genesis 6:3
God's Covenant With Noah: Promised - Genesis 6:18