Our goal as Christians is to become like Christ. Like a man and woman who form a family with the characteristics they subconsciously choose to share with each other, taking on the character and mannerisms of Christ comes naturally out of joining His family. As He is holy, we should strive to become holy; as He lives for others, we should strive to live for others; as He obeys the Father, we should strive to obey the Father.
The warning Christ gives to His listeners to not be left outside is a reality check for those who think they can offer the Lord the minimum and still enter Heaven. If the Master doesn't know us, why should He let us in? And He won't know us unless we strive to know Him. We become like the ones we spend time with and love and seek to know. If we're not becoming more like Christ Jesus, we're not investing in our relationship with Him. And if we're not investing in that most important of all relationships, we won't be recognized and welcomed into His home at the end of our lives and at the end of the ages.