John here calls the 
Religionists of his day offspring of vipers, no doubt referring to their being in the service of Satan, the original serpent. (
Rev 12:9 of 7-12) The people he was talking to were descendants of Abraham and a part of  
Judaism; which had been the previously acceptable form of worship to the One True God. Christ was replacing Judaism with Christianity; 
choosing people who would worship God in 
spirit and truth. (
John 4:7-26; 
Gal 3:7-14) So, John told them not to rely on what they and/or their forefathers had previously thought, and some among them defiantly continued to think, was acceptable to God. (
Mat 15:8-9) Like all of us today, they needed to listen to and put faith in Christ... Remaining part of what they had now, by rejecting Christ, turned into a 
religious sect would no longer help them. It will not help you. Religionists try to do you great harm. (
Mat 24:11-14; 
Pro 1:10-15; 
Rom 16:17-20; 
Exo 23:1-3) To please our Father and gain life, you have to be a friend of Christ. (
John 15:14 of 11-16) You can only become Jesus's friend by sitting at his feet; by reading his words over and over (
Mark 3:31-35) to familiarity. (
Matthew, 
Mark, 
Luke and 
John) The fact you read them once or twice some time in the past might not qualify you as his friend... That is between you and God, of course! (
Mal 3:16-4:3)