I agree.... and I think that by "persevere" we are to continue in our walk with Christ... which does NOT mean we will never sin again, it simply means our shortcomings and failures are covered with the grace of God.
Like was stated earlier, it's when we willfully walk AWAY from God, no longer desiring a relationship with Him, that we lose our salvation.... the "unpardonable" sin. God will not FORCE forgiveness and salvation on us. If we CHOOSE to reject Him, that's unpardonable.