John wrote three letters that address false teaching concerning the person of the Messiah and concerning the basis of righteousness.
1 John 1-2, We Have Touched With Our hands
John is writing to address heretical confusion sown among believers as to the nature and person of the Messiah. He starts by stating that he has personally seen, heard and touched Y'shua.
1 John 2, No New Commandment
John speaks of the Torah as both an old commandment and a new commandment. In this view, the text has not changed but our understanding of it must be adjusted in light of the sacrifice of Y'shua. His light shines upon us and allows us to understand the spirit of the Torah as well as the letter.
1 John 2-3, Children of God
The love of the Father and the sacrifice of Messiah has allowed us to be children of God. In this we are, in a sense, estranged from the world because He was also.
1 John 3-4, Love Your Brother
Loving your brother is practical, not ethereal. So if your brother has worldly needs, you shall not close your hand against him. This is Torah 101.
1 John 4-5, Abide in God
John speaks of Messiah abiding in us, we in Him and we in God. The criteria for this are belief that Y'shua is the Son of God who came in the flesh and obedience to His commandments.
1 John 5, Keep Yourself from Idols
John closes his first letter with what seems almost like a throw away line, "Little children, keep yourselves from idols." Far from being a non sequitur, that line summarizes the entire letter.
2,3 John, Christian Hospitality
In both of these two short letters, John speaks of the duty and limits to Christian hospitality. In one he warns against extending hospitality to those who would sow confusion about the identity of Messiah and in the other he commends hospitality to missionaries.