Jesus promised to send the Holy Spirit (see also 14:16; 15:26; 16:7, 12–14).
The Holy Spirit … will teach you all things: The Holy Spirit will teach the disciples everything. He will help them remember the words of Jesus and understand what those words mean. John experienced this help from the Spirit as he wrote his gospel (2:22). Christians also experience this work of the Spirit as they hear and study the Scriptures.