This is a technical term. "Heaven and man" is actually equal to three places: the human world, the Ashura world and the heaven world, because in the six divisions of the wheel of karma, the life in these three places has high spiritual wisdom, which is recommended by Buddhism and also called "three good ways/three good interests". This sentence means that if you practice to the point of freedom of life and death, there will be three good creatures to provide good conditions to help you practice (that is, support).