This is the day.

Exodus 7:3 And I will harden Pharaoh's heart, and multiply my signs and my wonders in the land of Egypt.
Exo_7:13 And he hardened Pharaoh's heart, that he hearkened not unto them; as the LORD had said.
Exo_7:14 And the LORD said unto Moses, Pharaoh's heart is hardened, he refuseth to let the people go.
Exo_7:22 And the magicians of Egypt did so with their enchantments: and Pharaoh's heart was hardened, neither did he hearken unto them; as the LORD had said.

The prevailing theme of all of these verses is that Pharaoh's heart was hardened. It doesn't take a whole lot for someone to harden their heart against God. It only takes a measure of unbelief, a measure of rebellion, and some self-will. Its hard to tell how many people have, at one time, been tender toward the Word of God, and have decided not to take an opportunity to trust in Him. The next time it got even easier to shy away from God, until finally their heart was hard against the Lord. We should strive to be tender to every nudge of God, and to be close to Him so that we don't develop that hardness that Pharaoh had. Yes, even a Christian can get hard against God. May we always be toward God as little children, and endeavor to never get as "wise" as Adam and Eve decided that they wanted to be. Your heart does not have to be hard! God will give us a chance to accept what He has for us if we will only be tender toward Him.