Everybody can learn to say the right things in a nice way to make a good impression.  Many do just that.  It is the stuff of sales and marketing, job interviews and romantic encounters.  Most families adhere to a code of acceptable speech, and so do most groups in society including churches.  So, we learn how to stay included, by what we say.
 
Jesus probed under the surface of human conversation.  How does anyone know what a person is really like?  The answer is simple: just listen to them for enough time (Ecclesiastes 10:12).  When the polished performance has worn off, you will hear what is in their heart, because eventually they will tell you.  That is the art of investigative journalism or legal cross-examination.  What is stored up in the heart will eventually be verbalised through the mouth (Matthew 15:18-19).
 
Of course, words are only a part of the 'fruit' of a person's heart: but they are key evidence of what lies under the surface of their personality.  Our hearts are like pressurised containers; what we store there, and think about, will become obvious eventually because we will talk about it, good or bad.  If that is true here on earth, how much more so when we have to tell the truth to Jesus Christ on the Final Day (Romans 14:10-12).  We will not be able to manufacture a nice story of our life of service for Him; instead, we will have to tell Him everything that is in our hearts (Hebrews 4:13).  Our eternal destiny will be determined by our own confession, including the reality of our relationship with Him.
 
If we are to tell Him of our repentance of wickedness and desire for holiness, then we need to be changed inside.  However religious we may be, this applies to us as much as to the religious leaders who first heard these words of Jesus.  Everybody who has accepted the Holy Spirit’s conviction of their sin, and have repented … they are the people who are grateful that Jesus has died so that they could be forgiven, and are glad that He has changed their heart.  They will be welcomed.  The others will not.  So let us not be like hypocrites who act out a story which will please their audience.  We need changed hearts which will overflow in words of truth, worship and praise to the Lord.