"Vayakam Bilam Vayeilech Vayashav Limkomo V'Gam Balak Halach LiDarko." (Balak 24:25). Bilam and Balak just witnessed amazing miracles and Hashem's divine protection for his beloved nation. Bilam had a conversation with a donkey and had words put in his mouth, despite the incredible lengths he had gone through to muster up the forces of evil to back his diabolical plan.
He lost his bid, but was not moved one bit. He did not tip his hat and graciously bow out. The whole experience did not change either him or Balak one iota from their former beliefs. Bilam went and returned to the exact place in his life where he had been before the incident, and Balak went back to his old path. How can these Reshaim have been so hardened and unmoved?
The Pninim Mishulchan Gavo'a brings in the name of Rav Eliyahu Mishkovsky that we see from here the little impact that open miracles have in moving a person to tshuva. Change does not come from instant revelation. Change is about noticing the little things in life. It is about opening your eyes to a fresh new outlook. These things have a far greater impact than lightening and thunder.