After the third plague, the Lord changed tactics. To make it even more clear to Pharaoh and all of the officials that these were no naturally occurring events, the next plagues – the flies, the death of livestock and the boils – affected only the Egyptian people, leaving God’s people unharmed.
Yet Pharaoh’s heart remained hard. In fact, after reading many times that Pharaoh hardened his own heart, now in 9:12 we read that the Lord himself hardened Pharaoh’s heart.
The Lord had told Moses that this would happen, back in Exodus 4:21 and 7:3, but why would the Lord do this? The answer lies in Pharaoh’s own stubbornness. In order for Pharaoh to obey the Lord, he first had to admit the sovereignty of the Lord, but he was too proud to do this. Despite all the evidence, he preferred to close his eyes to the obvious truth. He hardened his own heart against God and against God’s people.
Think about the effect of the sun on a piece of wax. The warm light of the sun softens the wax, making it easily shaped into a light-giving candle. Now think about the effect of the sun on a piece of clay. The warm sun dries and hardens the clay, making it stiff and impossible to shape. The sun is the same, but the effect is completely different.
When the light of the Lord shines onto a willing heart, that heart softens and shapes to the Lord’s will, but when a person has already hardened their heart, the light of the Lord has a completely different effect. Pharaoh had worked so hard to harden his own heart that any exposure to the sovereign God only resulted in even more hardening.
There are many reasons why a person might harden their heart against the Lord – fear, pride, disappointment, hurt – but when we confess our situation and repent of it, then the Lord can soften our hearts like wax, ready for the imprint of his love and life.