There are only a few “completely unfamiliar” words in the Church Slavonic language; You must definitely find out their meaning and try to remember them. But often we simply cannot make out that an unfamiliar word is one of the forms of a familiar word. Slow, thoughtful reading, even without a dictionary, will help you recognize “acquaintances” in some “strangers,” feel the connections of a word with other words, and thus understand its meaning. And the more you pray in Church Slavonic, the more carefully you listen to the words of the service, the more steadily the number of “blank spots” in your Church Slavonic vocabulary will decrease.