Usually Aquinas tries to find a lot of objections towards his hypothesis but he only finds two against the existence of God; evil and science.  Out of those two, only evil claims that a divine being does not exist. Regarding the other, people say that there is no need for a God when science can explain everything.

The problem of evil can simply be explained like this. If God is omnibenevolent, then evil should not be discoverable on the face of the earth due to the fact that a good God cannot coexist with evil in the world. Since there is evil on the earth, God cannot exist.

Aquinas tries to justify this by showing that “As Augustine says, ‘Since God is the highest good, He would not allow any evil to exist in His works unless His omnipotence and goodness were such as to bring good even out of evil.’ “ (Summa Theologiae 1,2,3). Notice the word “allow” in Aquinas’ answer, he does not state that God is the creator of evil. God did not create sin, but rather created human beings with free will. God does not kill, he creates beings that are finite. “When we come to moral evil, or sin, Aquinas’s explanation for God allowing it is to preserve free will and to bail us out of our sin by the supreme act of love, giving His life to save us.” (pp 23)

Aquinas shows that science cannot explain everything. Just looking at Aquinas’ principles for showing the existence of God to an extent shows that some things cannot be explained at all save for faith (cf. Lecture 3 First Way)

Five Objectives to the Quinque Viae

Can one really trust someone from an era in which science was not the best that it could have been?

It seems that back in Aquinas’ day that some things had not been discovered by science, such as (in context of First Way) that an object in motion tends to remain in motion unless acted on by another or that space is a vacuum so that a planet could be in motion around a star forever if it had a stable orbit, without being pushed by another force. “But Aquinas’s first way doesn’t move on this scientific level but on a metaphysical level. Aquinas did not mean by “motion” simply “motion through space” but any kind of change; and his proof that nothing can move itself does not depend on the physical concepts of momentum or drag or vacuums, only on the metaphysical concepts of potentiality and actuality.” (pp 24)

Can logic be applied to God?

That statement in and of itself itself is a contradiction. To say that you cannot make a logical statement about a being is false. Because the very thing that it is, is a logical statement.

But how come God does not need a cause?

This sentence in and of itself would be illogical. It would also be the same as saying “who made the unmakeable maker?” The definition of God is that God is an unmoved mover.

But does that mean it is a contradiction, Aquinas said that all things need a mover however, God does not need a first mover?

This is a poor objection as Aquinas said that: “He says that everything in motion needs a cause, everything that begins to exist needs a cause, everything contingent needs a cause, everything imperfect needs a cause, and every unintelligent being that acts for an end needs a cause.” (pp 26)