Death of the Egyptian Firstborns
Rabbi Reuven Mann, quoting shiur from Rabbi Israel Chait
Rabbi Chait said Macas Bechoros was unique. Every other maca came through an angel, i.e., a visible, physical force. For example, a great wind preceded the Arbeh, and the first maca - plague - (Nile River turning into blood) involved producing some change in the water and so forth. Every maca expressed itself via a change in some visible physical phenomenon. Macas Bechoros however was direct. There was no medium through which it expressed itself that was apparent to the Egyptians. Until now all they saw was that G-d had some type of control over the physical forces of nature but that He was limited in that He had to operate through them. Thus, there was some measure of safety and possible escape. He couldn't just will me dead with no apparent cause which I could trace to some element in nature. So before, G-d always operated within nature, so to speak, but in Macas Bechoros, He revealed an entirely new dimension - outside of nature - by which He can strike you down at will. Hence, the terror of that night was different than that which attended any other maca. This is my understanding and explanation of what I heard on the taped shiur.