I John - fellowship with God is life, light, and love.
"If we walk in the light... we have fellowship with one another"; "He that hath the Son hath life". "Beloved, let us love one another: for love is of God."
2 John - Encouragement in truth and love.
The Apostle John writes to the "elect lady and her children whom are loved by him and "all that have known the truth." "I rejoice greatly that I found thy children walking in truth" "that we love one another."
3 John - Christian hopitality.
"[Brethren and strangers] have borne witness of thy charity...they went forth, taking nothing of the Gentiles...we ought to receive such that we might be fellowhelpers to the truth".