If someone is kind to everyone else but snarky and rude to you when no one else is looking then you know the character of that person but the others who only see their happy side do not know them.
A kind person is that way all the time to everyone. They do not have one persona for those they wish to impress and another for those they hate.
In fact, kind people do not hate people, they demonstrate respect to everyone because there is love in their hearts.
1 Corinthians 13:4-7
"4 Love is patient, love is kind, it is not jealous; love does not brag, it is not arrogant. 5 It does not act disgracefully, it does not seek its own benefit; it is not provoked, does not keep an account of a wrong suffered, 6 it does not rejoice in unrighteousness, but rejoices with the truth; 7 it keeps every confidence, it believes all things, hopes all things, endures all things."
When someone has the character quality of love they are continually kind to everyone all the time. If a kind person unthinkingly acts a little rude for a moment they quickly apologize.
An unkind person never apologizes for their rudeness, they are ungrateful for kindness done to them as though it is owed to them. In other words, an unkind person is always about themselves, whether or not they are elevated above others. The slightest correction or indication of disapproval causes these narcissists to rave, exact revenge, use covert digs and pokes to get back at the one who dared to tell the truth.
Unkind people are not satisfied with appearing above others they must diminish and destroy others to achieve their self-elevation.
God was very clear about those who do not love anyone but themselves, they cannot be born-again unless they can learn to confess their flaws and desire to be cleansed by Christ.
Many people in our day claim to be Christian but will hear these terrifying words from God when they are thinking they have gained heaven:
Matthew 7:21-23 "21 “Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven. 22 On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?’ 23 And then will I declare to them, ‘I never knew you; depart from me, you workers of lawlessness.’"
May those who have not been born again but think they are, reflect on these words, repent and become born-again by the power of the Holy Spirit.
