When Noah set his first foot in the ark, he must have realized that this time he was not entering in order to continue construction. He was not entering to fine-tune the interior of the ark or smooth out the gopher wood. Instead, he was entering for the last time, and he would not be leaving any time soon.
Noah's wife. Shem, Ham, Japheth, and their wives. These seven people were part of Noah's household. Noah was entering the ark with them— he was entering the ark with those who he loved the most, trusting that they would be saved— trusting in the God who he loved to bring them to safety.
The animals also entered the ark:
they and every beast after its kind, and all the cattle after their kind, and every creeping thing that creeps on the earth after its kind, and every bird after its kind, all sorts of birds. So they went into the ark to Noah, by twos of all flesh in which was the breath of life. (Genesis 7:14-15)Just as Noah and his household would ensure the survival of the human race, so the animals would ensure the continuation of each of their species (see The Animals Come To Noah).
Once everything was in the ark, the moment must have come when everyone held their breath, trembling in expectation of what would happen next. Would the water immediately come? Just how rough would it be? Would it really be safe?
Whatever the questions might have been, they were answered by God Himself. God made clear from the beginning of the journey that He would be with them. He made clear that they would not be abandoned. In that final... climatic... moment... God Himself shut them in the ark. And in that moment, it was made clear that there would be no more mercy for the pre-flood world. They had already been given 120 years of mercy, but now... now there were zero years of mercy.
Zero More Years of Mercy (Part 1) - Genesis 7:16
The Destruction of The City of Enoch (Part 1) - Genesis 7:17-18
The Long Expected Rain (Part 1) - Genesis 7:10-12
Genesis 5:29 - Noah's Name: Its Meaning and Significance
State of the World (2349 BC): The Flood (Part 1) - Genesis 7:11