People will seem kind and from a good family, they will tell you sweet words, but you shall see their true heart from their deeds. Not words but deeds unveil your true heart. Anyways, many people heed to hide their passions and give the impression of good people but only on some occasions.

Use the friendship of people with a good character and let your soul delight with it. Do never turn your year away from their advice. Because their words are the words of life and the spiritual health thrives in those who seek it. As the sun that when it shines it casts away darkness, the teachings of the saints cast away the darkness from your thoughts. Do not avoid the companion of such people, so that, your mind may rise to Heaven, and prevent the glory of this world to defeat you. On the contrary, the virtues of the soul may captivate your mind.

Stay away from the people who ignore God’s commandments. Their virtues are dead and they live for passions. They live to satisfy their own will but are devoid of heavenly joy. This is the kind of people that you should stay away from and fear even to talk to them, unless they want to turn from their lost path. Otherwise, if you cannot help them, stay away from them as from your enemies. Very often, a rotten egg will compromise the entire dozen and a piece of gall will turn all the sweetness bitter (and the whole composition). This is the composition that the Lord tells you to avoid (Matthew 16:6). In this context, composition means the teaching of people with a bad character. At the surface, such people will seem kind and from a good family, they will tell you sweet words, but you shall see their true heart from their deeds. Not words but deeds unveil your true heart. Anyways, many people heed to hide their passions and give the impression of good people but only on some occasions. But since they nurture the snake in their bosom, affected by its bite, they swell and their true character is revealed, because there is nothing covered that shall not be revealed (Matthew 10:26).

(Sfântul Vasile cel Mare, Învățătură către fiul duhovnicesc, traducere de I. Popa, Editura Mitropolia Olteniei, Craiova, 2007, pp. 56-57)