“Unzo is deep and contemplative thinking… In dokuju (reading and reciting the sutra), whether chanting in shindoku or kundoku [or English], it is difficult to maintain deep and contemplative thought; during shodai, it is easy to maintain deep and contemplative thought.” Raiju-giki

Shutei Hoyo Shiki, page 272

When chanting in non-English, we can become so focused on getting the pronunciation correct that we get distracted. Chanting in English, we can get distracted by pondering what the words mean and trying to assemble a complete understanding. During Odaimoku, or shodai, we can become bored and our mind wander. Doing unzo beforehand helps us maintain our focus and reminds us of our intention. Unless a specific one is given, a suitable unzo is to read Nichiren’s instructions. Failing that, you may simply pause to focus your thoughts.