The Law of Cause and Effect is a Universal Law and applies to all, whether you believe it or not. It is like the Law of Gravity. Only with gravity , you can prove it, here and now.However, the Law of Cause and Effect plays itself out over lifetimes.For instance, the Cause or 'action' was performed in a previous lifetime and the Effect is experienced in this lifetime. Hence it's hard to convince anyone about it.
A family friend, who is a Muslim, is very rich.He was born with a silver spoon in his mouth. He has never had to work for anything. He never had to swot over exams to get a degree. Now , he is over 70 years of age and has never known a day's illness.His own brothers, on the other hand, have had to study to get professional qualifications so as to carve out successful careers for themselves; and now in their old age, they are sick and suffering. How came it that he alone is living the life of a samsaric god? But I know that I cannot convince him or any non-believer or non-Buddhist that he had created the causes for being a samsaric god in a previous lifetime or many previous lifetimes.
Personally,I am glad I have created the causes to meet with the Dharma in this lifetime and to meet with the King. I think it is rare for a person to have created the Karma (merits)to be born a human and to meet with the Dharma, a great Spiritual Guide, Lama Tsongkapa's teachings and the King Protector. Rare and more precious than to be born rich and a samsaric god like my friend. I fold my hands to the Three Jewels.