This text gains impact when we reconsider our writer's original audience. His heart is troubled when he sees the potential diluting of the faith of these Jewish believers. These followers of Christ have not yet changed their minds about Jesus, but the language of this letter hints they were weakening in faith. They had family and friends - and their previous religious associations - all urging them back into their Judaic faith.
There is a New Testament urgency to the exclusivity of commitment to Christ alone that is missed by our inclusive religious culture - Galatians 5:4 - "You are severed from Christ, you who would be justified by the law; you have fallen away from grace."
We may wonder why our writer keeps going over the same ideas in this letter, but you would too if someone you loved - perhaps someone you had led to the Lord - was being drawn away from gospel faith and gospel truth. Remember, our writer isn't trying to compose sermon texts for worshipers at Cedarview Community Church. He's trying to rescue the perishing. He's trying to rekindle and preserve gospel faith in his beloved hearers.