Petrarch's real subject is the vagaries and contradictions of the divided self.
Human love displaces divine love as the most important thing in life.
The Petrarchan experience:
Love is at first sight. It enters through the eyes into the heart and never goes away.
Love is never satisfied. The lady is unavailable, or hard-hearted, or changeable.
Love is suffering. The lover hopes that the lady will see his suffering and have pity on him, and give him her love. Sometimes the lover thinks that this miracle is about to happen, but it never does, and he is caught in a conflicted state, often stated paradoxically as "freezing fire."
Despite, or maybe even because, love is suffering, the lover stays true to love because he is helpless to do otherwise, and it inspires him to creativity (writing poetry), and because being in love makes life worthwhile.