Renaissance Humanism is applying man's reason to the explanation of what is and how to live ones life. This way of thinking came to the forefront in the 1400s and reached its zenith from that time to the mid 1600s. It involved a departure from religious beliefs to explain things, and promoted man's own ideas and viewpoints based on what he saw and felt. It did not rely on the unseen and unobservable, but only on what could be observed - and then pondered - which resulted in conclusions drawn that had nothing to do with belief in God, belief in gods, and faith. In essence, the creation, not the Creator, is the basis of Renaissance Humanism, and today Humanism.
Renaissance Humanism's outlook and drive was, and is today in its present form, pleasure now, freedom of choice to do what one wants, without any higher, spiritual moral code to oversee it. Human wants and desires, without a religious hierarchy "in the way" so to speak is at the heart of Renaissance Humanism, and Secular Humanism in general. However, this does not mean that Humanism is something that ignores the plight of man. Secular Humanism today often does promote taking care of others - ones fellow man - and doing good to others to promote a just and equitable society. The difference is, God is not in the picture, or more accurately, is left out of the picture. Man is the be all and end all, man is his or her own god.