Charles Ellicott Commentary Matthew 7:21

"Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father who is in heaven." — Matthew 7:21 (ASV)

He who does the will of my Father — The continued stress placed on the ethical side of religion, and on the worthlessness of confessing a true faith (as embodied in “Lord, Lord”) without doing the will of God, more than confirms the interpretation of Matthew 7:16 given above. A further development of this same thought is found in John 7:17. We are taught that it is by doing the will of God ourselves—or rather, by willing to do it—that we gain the power to distinguish truth from error and human teaching from God’s, to the extent that we need to.

The preceding words imply that the disciples had already begun to use the title “Lord” (Greek: kyrios) when speaking to their Master . However, since that word was in common use at the time as a term of courtesy (Matthew 8:2; Matthew 8:6; John 20:2), it does not necessarily follow that they used it with all the later fullness of its meaning.