John’s letter is about assurance of salvation—knowing God and knowing that He knows you, which results in fullness of joy: “And these things we write to you that your joy may be full”. He has expounded the great assurances of our salvation—walking in the light, loving the brothers, and believing in Jesus Christ—and now concludes by driving home three things the confident in Christ know and do: our prayers are effective; the one born of God does not fall away; and the Son of God has given us true knowledge of Himself, in Himself.