ANSWER: First, let us define our terms. Encouragement has the word 'courage' in it, and as such means to inspire someone to be courageous, hopeful, and confident. The basic definition of flattery is that it is excessive, insincere praise. It usually given in order to motivate someone to do or think something they might not otherwise do (to think well of or to help the person giving the praise, etc.).
In the Bible, flattery is not speaking words to help strengthen someone for their own sake, but speaking words to deceive and to cover the speaker’s motives. Encouragement is the TRUTH presented with good will toward others, while flattering is a LIE that seeks to use others.
Biblical examples of encouragement include Deuteronomy 1:38, 3:28, Judges 7:11, 20:22, and 2Samuel 19:7. A New Testament person widely known to encourage others is Barnabas (Acts 4:36). He played a pivotal role in spreading the gospel in the first century (Acts 9:27, 11:22, 13:2, etc.). Barnabas Ministries is the name of the independent ministry that owns and operates BibleStudy.org.
Flattery is in the Bible in several places, including the Psalms, Proverbs, the book of Job and elsewhere. Several Psalms (Psalm 5, 12, 36, 49, 78) equate the false words of flattering with lying, deceiving, hiding sin, and promoting wickedness. Job understood that such lying words were not something that was acceptable to God.
22. For I do not know how to give flattering titles to any man, else my Maker would soon take me away (Job 32:22, HBFV throughout)
Wise Solomon said the following about flattery.
23. He who rebukes a man shall afterwards find more favor than he who flatters with the tongue (Proverbs 28:5)
5. A man who flatters his neighbor spreads a net for his feet (29:5)
Lying words that kill
Like most leaders Herod Agrippa I, who ruled Galilee and Perea for the Roman Empire, loved to be flattered. There came a day, however, when the smooth words of others would cost him his life.
20. Now there was bitter hostility between Herod and the people of Tyre and Sidon; but with one accord they came to him (in Caesarea) . . . (Acts 12:20)
The Tyrians and Sidonians, fearful Herod could punish them by withholding much needed supplies, decided to flatter him in the hopes of calming the tension between them.
21. And on a set day, Herod, who had put on royal apparel, sat down on the tribunal and made an oration to them. 22. And the people cried out, "It is the voice of a god, and not of a man!" (Acts 12:21 - 22)
Herod, who did not have a record for being humble, no doubt reveled in the over-the-top praise. Rebuking the crowd for what was clearly false praise, meant only for the Eternal, was the furthest thing from his mind. His response, however, did get the attention of God.
23. And immediately an angel of the Lord smote him because he did not give the glory to God; and he was eaten of worms, and died (Acts 12:23).
Christians should always pursue honest encouragement toward others while shunning the lying words of flattery.