When we say that Augustine's style is personal, we mean that there are going to be a lot of "I's" in the Confessions. Probably more than most first-person narratives, even. This is because Augustine is talking about himself, yes, but it's also because Augustine wants to draw attention to himself, especially to his wrongdoing. His writing can read like a diary confessional. See, a diarist might say something like, "I felt really bad that I stole the pears, but I did it anyway because I wanted the others to think I was cool, I guess." And that sentence reveals a very personal feeling that the speaker has. Here's Augustine's version:
I loved nothing in it except the thieving, though I cannot truly speak of that as a 'thing' that I could love, and I was only the more miserable because of it. (II.8.1)
So, Augustine can sound all "me me me." But by being so personal, we're actually able to relate to a lot of what he says. Augustine sure can get you thinking about how you feel after doing something you know is wrong.
Here's the interesting bit about super personal writing: it's weirdly self-focused and relatable at the same time. Which is probably why we all love blogs so much.
The other side of Augustine's writing style crops up when he talks about philosophical ideas, like the creation of the universe and big things like that. He loves to ask questions that slowly build toward a conclusion:
In what way, then, do you, Ruler of all that you have created, reveal the future to the souls of men? You have revealed it to your prophets. But how do you reveal the future to us when, for us, the future does not exist? Is it that you only reveal present signs of things that are to come? For it is utterly impossible that things which do not exist should be revealed. (XI.19.1)
Or, he'll propose an idea based on a concept that he has already established as true:
It is therefore true to say that when you had not made anything, there was no time, because time itself was of your making. (XI.14.1)
You'll probably notice a lot of Socratic Method "If… then"-type action as well. (Augustine was trained in rhetoric, after all.) But Augustine's analytical reasoning isn't just limited to the "analysis" books (Books XI-XIII). He uses this writing style during his discussions of Manichaeism, God's substance, and so on in the actual narrative, too.
In short, because Augustine is a professor of rhetoric, he can make language do pretty much whatever he wants it to do. But he's not trying to be a shady lawyer about it. He just wants to use the skills God gave him to do God's will: to get people to give up their sinning ways and convert to Christianity. So, when reading Confessions, try to pay attention to how Augustine articulates himself, not just to what he says. Actually, that's just English 101 for ya, Shmoopers.