If Christ died on the cross for all of humanity

First, he argues that the chain of movers must have a first mover because nothing can move itself. (Moving here refers to any kind of change, not just change of place.) If the whole chain of moving things had no first mover, it could not now be moving, as it is. If there were an infinite regress of movers with no first mover, no motion could ever begin, and if it never began, it could not go on and exist now. But it does go on, it does exist now. Therefore it began, and therefore there is a first mover.

Second, he expands the proof from proving a cause of motion to proving a cause of existence, or efficient cause. He argues that if there were no first efficient cause, or cause of the universe's coming into being, then there could be no second causes because second causes (i.e., caused causes) are dependent on (i.e., caused by) a first cause (i.e., an uncaused cause). But there are second causes all around us. Therefore there must be a first cause.

Third, he argues that if there were no eternal, necessary, and immortal being, if everything had a possibility of not being, of ceasing to be, then eventually this possibility of ceasing to be would be realized for everything. In other words, if everything could die, then, given infinite time, everything would eventually die. But in that case nothing could start up again. We would have universal death, for a being that has ceased to exist cannot cause itself or anything else to begin to exist again. And if there is no God, then there must have been infinite time, the universe must have been here always, with no beginning, no first cause. But this universal death has not happened; things do exist! Therefore there must be a necessary being that cannot not be, cannot possibly cease to be. That is a description of God.

Fourth, there must also be a first cause of perfection or goodness or value. We rank things as more or less perfect or good or valuable. Unless this ranking is false and meaningless, unless souls don't really have any more perfection than slugs, there must be a real standard of perfection to make such a hierarchy possible, for a thing is ranked higher on the hierarchy of perfection only insofar as it is closer to the standard, the ideal, the most perfect. Unless there is a most-perfect being to be that real standard of perfection, all our value judgments are meaningless and impossible. Such a most-perfect being, or real ideal standard of perfection, is another description of God.