This is the purpose for which the Holy Prophet had been sent. He was entrusted with the mission that he should bring mankind back from the ways of darkness (ways of wickedness) into the Way of God by the help of the Light of the Qur'an. For everyone, who is not on the Way of God, is, in fact, wandering about in the ways of the darkness (of ignorance), even though he might consider himself to be very enlightened and full of knowledge. On the other hand, the one who finds the Way of Allah, comes into the Light of Knowledge, even though he might be an illiterate person.
As regards "by the help of their Lord", this implies that the most a missionary of Islam (even though he be a Messenger of Allah) can do is to present the Right Way. It is not in his power to bring anyone forcibly to the Way, for this can only happen by the help and permission of Allah. That is why only that person whom Allah helps and permits gets guidance: otherwise even a perfect Missionary like a Messenger fails to bring a person to the Way. As regards the Divine Law, according to which Allah helps and permits a person to gain guidance, we learn from different passages of the Qur'an that Allah gives help only to that person who himself has a desire to get guidance: who frees himself from obduracy, obstinacy and prejudice: who is not a follower of his lust, nor a slave of his desires: who is inclined to see with open eyes) and hear with open cars and think with a clear mind, and is ready w accede to any reasonable thing.
The word (Hamid) is more comprehensive than (Mahmud). A person will be entitled to be Mahmud only when he is praised. But the Being Who is Hamid, is naturally and permanently worthy of praise, whether anyone praises Him or not, because the element of praise is inherent in Him and is inseparable from Him.