John 1:7 means you can go directly to heaven, but do you truly believe you walk in the same light as Christ. Are you truly free of sin and the tendency towards sin. Do you hold nothing back for yourself? Maybe you do... But that verse hardly disputes that purgatory exists.
2 Maccabees 12:46: “Thus he made atonement for the dead that they might be freed from sin.”
It would have been foolish to pray and make sacrifices for those who had died if they were already in hell or heaven.