But his impression of the community was "very split".
"It's not a lifestyle I would choose. But in actually talking to a lot of the people that are there I couldn't help thinking, 'They have a happier and simpler life than I do.'
"I looked at a lot of the kids, and I thought, 'You're not going to be teased in school because you've got the wrong Nikes on, and you're not going to be logging into Facebook and getting people telling you you're fat.' So I thought, okay, there's something."
The people living in Gloriavale were "treated very well", he said.
"Their day-to-day is not very complicated. They get up, they work - very gendered roles, based on the Bible, the men do a lot of work, they've got a lot of businesses there, the women spend a lot of time sewing or in the kitchen - and then they get together in a big dining room all together for meals."
There was no deprivation in the community, he said, and the wealth and products of their labour appeared to be equally distributed among the families.
It was "not like going back in time", because unlike the Amish religious community in the United States, the residents of Gloriavale used modern technology and industry for their work and businesses.
"They certainly have electricity, they certainly have heating, they don't really want for any of the necessities," he said.
What the Gloriavale community was doing was not unusual in a global context, he said, but appeared to be "an oddity" for New Zealanders.
"The whole idea of what they're doing is not new at all - there's the Hutterites, Mennonites, the Amish, it's all based on basically the same thing.
"You could set up a Christian community in almost any state in America, the neighbours would bring apple pie and get on with their business. That would be quite normal, but in New Zealand it's a bit of an oddity."
This was why Gloriavale could not be described as "a cult", Mr Sepie said, because its ideology was based on the Bible and Christianity.
"The main fundamental rule of a cult is it must develop its own ideology and religious doctrine, they [Gloriavale] are using Christianity - that excludes them from being a cult ... By a technical definition they could never be a cult," he said.
"All they can be called is a sect. They're fundamentalist Christians at heart, that's it."
However, he said he understood why "people are having the reaction they're having" to Gloriavale.
"When I went in there the first time I was [thinking], 'Okay, what am I going to find,' and then it's when you come to understand something a little more [you think], 'That's cool.'
"As a sociologist I'm quite well aware of what New Zealand society accepts and doesn't accept. We are the most irreligious country in the world, even though 50 per cent of us are Christian. So some secluded community sect sets off alarm bells for people."
But there was nothing for people to be concerned about, he said, the Gloriavale leaders were not "masking anything sinister".
"Things happen in all places, but picking apart dirty laundry to say that everything's wrong is just a little unfair. They are human beings, they have lives, and they actually look like they enjoy their lives. And if they don't - and some of them haven't - they leave," he said.
"I think the danger is picking too much at something and imploding it. If there was enough pressure or somebody was to somehow pull the pin, what would 500 people do? Without jobs? And not knowing what society was like? What would they do and who would pick up the pieces?"
