A literary ending for a vow or a confident prediction: it will come to pass as spoken, I am sure you all know, I will give it a go. In modern use it appears mostly inside 리라 믿다, meaning I trust that it will, which four of these lines do, or as a charm you say to yourself, as in the caption about telling yourself you will do well today. It sounds scriptural, so it carries solemn or mock-solemn weight.