What makes a 'homily' different from an 'aphorism'?

Homiletics is the study of the art of preaching. A homily is specifically an instance of preaching and can refer to an entire sermon or it can refer to a shorter discourse, typically edifying in nature, for spiritual uplift, rather than a theological discourse to communicate information. The word "homily" is also used pejoratively to refer to a preachy or judgmental spiritual message, or even "preaching to the choir".

Used in a sentence, one might say of a person, "He speaks in homilies instead of offering spiritually sound reasoning."

On the other hand, an aphorism is a short saying that communicates a general principle, such as, "Early to bed, early to rise, makes a man healthy, wealthy, and wise." Aphorisms can be proverbs, witticisms, rules to live by, and observational. They are short and self-contained sayings with a point, while homilies can be short, or they can go on for hours.