I was being vague in "follow Christ" but specifically that means recieving His sacraments. Only through His sacraments can we be saved as through Him we become more perfect as our Heavenly Father is perfect. Baptism is necessary, confession if fallen into mortal sin is necessary, communion is necessary. You are correct in saying that most "Christians" will say "Lord, lord" but be devoid of the sacraments and live in mortal sin and thus be deserving of The Judgement. This is the ancient understanding of "following Christ" corroborated by writings from apostles, early church fathers, all the way to Thomas Aquinas and later.