Writing a commentary essay on a character, such as Friar Laurence, will be a cross between a character analysis essay and a literary analysis essay. It will be like a character analysis essay because your first step will be to analyze the character; it will be like a literary analysis essay because you absolutely will not want to just summarize the text or the character but instead focus on literary devices, such as theme, conflict, imagery, symbolism, paradox, etc. Here are the differences between a character analysis essay and a commentary on a character: 1) In a character analysis your one goal is to define exactly what that character is like and determine the character's traits through the character's words, thoughts, actions, motives, etc.; 2) While you'll start with analyzing the character for a commentary, your ultimate goal will to comment on what the character's deeds, thoughts, motives, characteristics contribute to the work as a whole, or what the author's purpose was in portraying the character in the way he/she did. In other words, for your character commentary you'll be analyzing how Friar Laurence's character traits contribute to things like theme, conflict, mood, and voice, etc.
For example, we could look specifically at Friar Laurence's reactions to Romeo's desires to marry Juliet so soon and how his reactions contribute to the theme. One of Friar Laurence's responses is to accuse Romeo of being fickle and being too young to truly know what love is; yet, he agrees to marry the couple anyway. Why? One of the most important themes in the play is intense, irrational emotion vs. rational thought. Many things Friar Laurence says in response to Romeo help illustrate this theme, especially Laurence's comment just before he marries them about how violent passion often comes to a violent, sudden end:
These violent delights have violent ends
And in their triumph die, like fire and powder,
Which, as they kiss, consume. (II.vi.9-11)
In saying this, he is warning that their love is not really the purest, strongest kind of love, but more like an infatuation that is doomed to end suddenly. He is saying that their emotions are intense and their actions are irrational, which illustrates the part of the theme concerning intense, irrational emotion. However, what's interesting is that, while Laurence had the sense to realize this, he did not have the sense to try and dissuade them from marrying so soon. Friar Laurence was also swept away by his own intense feelings concerning wanting to end the feud. We learn that Laurence's motive for agreeing to marry them so hastily is his belief it will put an end to the feud in the earlier scene when he says:
In one respect I'll thy assistant be;
For this alliance may so happy prove
To turn your households' rancour to pure love. (II.iii.93-94)
Hence, if we note the fact that Friar Laurence really felt the marriage was unwise but did it anyway because he felt their was a more significant motive, then we see that even Friar Laurence let his intense emotions on a subject override his more rational thoughts, which perfectly illustrates the theme of intense, irrational emotion vs. rational thought.
Therefore, if we were to comment on Friar Laurence's words and actions in Scene 3 and 4 of Act 2 alone, we could show in many ways how Friar Laurence's characterization illustrates theme, as well as other things, such as conflict.