"The one who believes in the Son of God has the witness in himself; the one who does not believe God has made Him a liar, because he has not believed in the witness that God has borne concerning His Son.  And the witness is this, that God has given us eternal life, and this life is in His Son.  he who has the Son has the life; he who does not have the Son of God does not have the life.  These things I have written to you who believe in the name of the Son of God, in order that you may know that you have eternal life."

John tells us that belief in God is our route toward inviting Jesus into our hearts.

If we believe in the Son of God, we live.  If we do not, it is the same as calling God a liar (a true sign that we do not understand God nor embrace His life for us.)

But then, John dives us a glimpse at his reason for writing this epistle:  John tells us he has written so that we may KNOW we have eternal life.  It is as if John has dealt with people that have eternal life, but do not live like they do. 

We are out of practice when it comes to living like we have eternal life.  Belief is the way in which we engage the eternal in us.

John is asking us to believe.

If you seek righteousness - seek belief in the One who gives life.