This brother took shahada with us (at Nov. 28) in Canada, he didn’t require any fancy arguments for the existence of God, he knew deep inside the Allah existed, all he need was the revelation of Allah the Quran.
when I approached him he looked sad, after speaking with him for a while he told me he was going through some really hard times. Alhumdulillah Allah allowed me to remind him of the fact that the happiness and peace he was searching for could not be attained by running after the dunya. After he understood that he was only going to find true peace by remembering Allah and submitting to him Allah allowed him to take his shahada.
I guess what we can take from this is that, deep inside people know Allah exists it’s the fitrah. All that needs to be done is to remind people, making them aware of the fact that true peace, happiness and freedom is only attainable through remembering, worshipping and submitting to Allah. That’s how we have been created.