The testimony of John concerning the Holy Spirit is unique in all Scripture. His discourse has five sections referred to the Spirit (Parákletos), the last of which is John 16: 12-15. In this section, in a particular way, the term “truth” is interrelated with the nature of the Spirit and his work. Likewise, the use of the verb “to guide”, referring to his guiding work, is opposed to the dualistic ontological use of Gnosticism. This study analyzes this last section that, when connected with the whole discourse and having as a framework the biblical thought of the OT, reveal the nature and work of the Spirit.