What the danger is about hellos (the sun of God's) cattle?

It was agreed that Odysseus' men would not touch the god's cattle, but eventually the men broke that agreement because they were starving. While trying to escape punishment, Odysseus' men were annihilated by a lightening bolt sent down by Zeus. Odysseus was the only survivor, as he was the only one of the men not to have taken part in the slaying.