A selection of verses illustrating that we should not be “two-faced”.
The prophet Ezekiel talks about insincere people, who say pleasant things, but really are selfish hypocrites:
31 They come to you as the people come, and they sit before you as my people, and they hear your words, but don’t do them; for with their mouth they show much love, but their heart goes after their gain.
The Psalmist says some people flatter and lie:
36 But they flattered him with their mouth,
and lied to him with their tongue.
37 For their heart was not right with him,
neither were they faithful in his covenant.
Jesus speaks about the hypocritical scribes and Pharisees in very unflattering terms:
27 “Woe to you, scribes and Pharisees, hypocrites! For you are like whitened tombs, which outwardly appear beautiful, but inwardly are full of dead men’s bones, and of all uncleanness.
6 He answered them, “Well did Isaiah prophesy of you hypocrites, as it is written,
‘This people honours me with their lips,
but their heart is far from me.
7 But they worship me in vain,
teaching as doctrines the commandments of men.’
8 “For you set aside the commandment of God, and hold tightly to the tradition of men—the washing of pitchers and cups, and you do many other such things.”
39 The Lord said to him, “Now you Pharisees cleanse the outside of the cup and of the platter, but your inward part is full of extortion and wickedness.
The apostle John says that our love for our fellows is to be shown in deeds not just in words:
18 My little children, let’s not love in word only, or with the tongue only, but in deed and truth.