I John 5  John repeats the words, "..we know".. 6 times in this passage.  His focus seems to be that we KNOW what we believe.

"Whoever believes that Jesus is the Christ is born of God..." (v1)  The phrase "born of God" was also used in I John 4:7, " .. and everyone who loves is born of God and knows God."  Both believing and loving, then, have their beginning.. their genesis, if you will, their birth ... in God.. "of" God.  Verse 1 of chapter 5 goes on to say, " and whoever loves the Father loves the child born of Him." 

"By this we know..."  Here is the first of John's "we know" statements.  Love for others, for the "children of God" is produced when we "love God and observe His commandments." (v2).
Loving God is defined by John ( and by Jesus.. John 14:21) as keeping His commandments.
Believing
Loving
Obeying
This is what we do when we are "born of God". 

As those born of God we:
"overcome the world" ( v4)
"receive the witness of God"(v9)
have "eternal life" (v11)
have "confidence.. before Him, that if we ask anything according to His will, He hears us." (v14)
stop sinning continually ( v18)
are protected by Christ from the evil one (v18)
are given "understanding... to know Him who is true", to be in Him ( the Father) and in Jesus. (v20)

As those born of God we know.. 
that sins loses its power over us (v18)
we are of God (v19)
"that the Son of God has come" (v20)
We know Him.. (v20b)


Father, once again we come before You, humbly seeking understanding and grace, to know You, to be filled with Your Presence, by the Spirit of God.. in all truth, wisdom, and love.  Thank You for loving us completely.  May our lives be one with Christ and with You, our Father, in mutual abiding.  May we know Whom we have believed!  May we love You with all of our hearts, minds, souls, and bodies.  May we obey Your commandments.  May we love others as You do. Take us deeper, draw us nearer and help us live so as to please You. For we ask it according to Your will and in the Name of the Lord Jesus Christ. Amen.