The chanting of the ancient Buddhism and present Mahavihara Theravada is for memorizing and revisit the practices again and again until getting the understanding to practice perfectly and reaching the mundane and super mundane attainment concentration (Lokiya-Appana Bhavana and Lokuttara Appana Bhavana). After that, the Buddhist still chant to revisit the way to teach by the buddha and to be a model for previous Buddhist.
Some chants are for building the encouragement to practice for attaining the concentration follow the Buddha such as "Itipiso Bhagava (Buddhanussati)" because the meaning of them are very deep in detail. The detail of is an enlightenment which has the perfect relations like Abhidhamma which is big data), so the practitioner will can't understand them easily at first. However, chanting still helpful without understanding because when the practitioner can't practice follow the Dhamma perfectly, if they can't remember the teaching, except they don't want to be perfect like the Sanga. And the practitioner can accumulate the wholesome trust while chanting as well. It is one of five elements to get the attainment.
(This should be the first: http://chanting-book-for-buddha.blogspot.com/2013/04/5-aradhana-tisarana-pancasila-request.html)
12.45 It is the pali about giving gifts to the Sanha. I think this chant is using only in thailand. The other countries may use something different.