In the Bible, it is stated again and again that the human race will be judged “according to what they have done.” (e.g. Proverbs 24:12; Revelation 20:12,13). However, we know that on this basis alone we would all be condemned, because we are all sinners. What makes the difference between condemnation and acquittal, then, is whether we know God. “Now this is eternal life: that they know You, the only true God, and Jesus Christ, whom You have sent.” (John 17:3) We can’t deserve God’s favour; but we shall be judged as righteous through our faith in His Son Jesus. “If you declare with your mouth, ‘Jesus is Lord!’ and believe in your heart that God raised Him from the dead, you will be saved.” (Romans 10:9)
However, “Not everyone who says to Me, ‘Lord, Lord,’ will enter the Kingdom of Heaven, but only the one who does the will of My Father who is in heaven.” (Matthew 7:21) It takes more than words to declare that Jesus is Lord (I Corinthians 12:3). It is sadly possible to attend church regularly, know all the orthodox ‘jargon’, sing the hymns and go through all the rituals – and yet not know Jesus at all. It appears to be possible to have a ‘successful’ Christian ministry and yet not be a genuine Christian (Matthew 7:22,23). It may even be possible to cast out demons, and yet be outside the Kingdom yourself (Luke 10:20).
To call Christ ‘Lord’ should mean that we submit to His Lordship. If we are claiming to have a relationship with the God “who exercises kindness, justice and righteousness on earth “ (Jeremiah 9:23,24), then we should care about the same things that He cares about. But it is an insult to Him to say that we are at His command, and then to go about our daily lives as if He means nothing to us. And so Christianity is essentially a practical religion: genuine disciples are obedient (James 2:14). Which brings us back full circle: we also shall be judged on what we have done, because our actions are the proof of our allegiance. Religious words (e.g. reciting the creed and singing hymns) are no substitute for deeds.
We have to be very careful here. Jesus’ warning is meant to stimulate us to examine our own hearts and lives, not to put ourselves in His place and pass judgement on people who may express their faith differently from us. “The Lord knows those who are His” (II Timothy 2:19) – but to us it may be less obvious.