1, 2, and 3 John are short letters written by the Beloved Apostle. Here is the Read Scripture 9+ minute video that covers all three books.
NOTE: As with all studies, use what study tools you can to rightly divide the Word. Be a Berean, & recognize that sometimes folks will disagree on what they think they see or know in the Scriptures. Use history. Use context. Use research. Answer the question Jesus asked the scholars of His day--"How do you read it?" Don't just take someone else's teaching as the final truth. Read the Word for yourself, pray for wisdom from above, & study to show yourself approved. editor
In the 3rd Letter of John, The Apostle of Love had no problem dealing in hard truth. These PC days being honest and upfront with truth is often maligned and "spoken evil of." It is the hard hand of loving someone with truth that gives them a chance to turn around from dangerous or stupid choices. Truth is truth is truth, no matter if you want to believe it or not, but once it comes to light, you either choose to walk in that light, or to stay in darkness, playing the PC games. Heaven is real. Hell is real. Judgment before a holy God is real... Truth or soft feel-goods? John the Beloved had no problem walking and working with truth.