1John 3:14,15 We know that we have passed from death to life, because we love our brothers. Anyone who does not love remains in death. Anyone who hates his brother is a murderer, and you know that no murderer has eternal life in him.
Those who have been born of God have already passed from death to life. Jesus said, "I tell you the truth, whoever hears my word and believes him who sent me has eternal life and will not be condemned; he has crossed over from death to life." John 5:24
The evidence John speaks of here that a person has come to genuine faith in Christ, and has consequently passed from death to life, is their love for fellow Christians. Hatred for fellow Christians is akin to murder - just as John spoke of the Cain as a precedent for such.
Murderers, along with many other categories of sinners, do not have eternal life. To name a few: "the cowardly, the unbelieving, the vile, the murderers, the sexually immoral, those who practice magic arts, the idolaters and all liars— their place will be in the fiery lake of burning sulfur." Rev 21:8 Similar lists are found in 1Cor 6:9,10; Eph 5:5,6; Gal 5:19-21