The whole Christian life is summed up in this, coming to believe that Jesus Christ is God. That is why it is put here by John. Now John is going to move on to claims about heavenly food that can only be understood or believed if we accept Jesus as God. If Jesus is anything less than he claims in the next few verses the Gospel is worthless. This is also what the Christian life is for us, coming to believe more and more that Jesus is God. Only prayerful reflection and humble attendance at the sacraments can lead us deeper into this acceptance. That is why we must be on our guard against all sorts of pride and self sufficiency. These things block out the humility to see Jesus as to who he really is. John is developing his theme in a structured orderly fashion.