There are certain signs that come with being alive:  warmth, movement, breathing, pulse, etc.    And these signs occur together or not at all.  One of these signs doesn’t appear unless the others are also present.  So it is spiritually.  John is grounding his congregation in the basics.  What is being spiritually alive?  God births His life in us.  What are the signs that indeed we are born in Him?   The vital signs:   love for God, love for one another, obedience to God’s commands, believing Jesus to be the Christ and the Son of God and overcoming the world.