Shin would normally only erect a 【Barrier】, but he thought that he would be doubted again, no matter how much of a Chosen One he was. Therefore, he decided to use an item for interception. Although he understood that a Chosen One was outside of the norm, there was a limit for that, so it would be bad to show a power beyond it. He was worried about his uncertainty of that limit.
While he was at it, he didn’t forget to put up 【Wall】, since the danger was not necessarily comprised of only monsters.