You can tell by context and grammar and usage in the book, chapter and verse. And, you can tell by the Holy Spirit, which informs the spirit (conscience, intuition, communion) of the reader. The part that is missing in the unbeliever is the communion with God, the connection to God. You will get that once you believe in Jesus as your Savior from sin. There are many levels of depth within books, and over the years, that come as a result of grace, faith, the Spirit in your spirit, studying the Word, obeying God, trusting God, going through trials. The main thing God wants for you first is to recognize you are a sinner in need of forgiveness and salvation. Then believe in Christ as Savior. Ten thousand spiritual gifts and insights follow thereafter.