Psalm 12:2

Vanity they speak each with his neighbour, Lip of flattery! With heart and heart they speak.

Psalm 41:6

And if he came to see -- vanity he speaketh, His heart gathereth iniquity to itself, He goeth out -- at the street he speaketh.

Romans 16:18

for such our Lord Jesus Christ do not serve, but their own belly; and through the good word and fair speech they deceive the hearts of the harmless,

Psalm 10:7

Of oaths his mouth is full, And deceits, and fraud: Under his tongue is perverseness and iniquity,

Jeremiah 9:8

A slaughtering arrow is their tongue, Deceit it hath spoken in its mouth, Peace with its neighbour it speaketh, And in its heart it layeth its ambush,

1 Chronicles 12:33

Of Zebulun, going forth to the host, arranging battle with all instruments of battle, are fifty thousand, and keeping rank without a double heart.

Psalm 5:9

For there is no stability in their mouth. Their heart is mischiefs, An open grave is their throat, Their tongue they make smooth.

Psalm 28:3

Draw me not with the wicked, And with workers of iniquity, Speaking peace with their neighbours, And evil in their heart.

Psalm 144:8

Because their mouth hath spoken vanity, And their right hand is a right hand of falsehood.

James 1:8

a two-souled man is unstable in all his ways.

Psalm 36:3-4

The words of his mouth are iniquity and deceit, He ceased to act prudently -- to do good.

Psalm 38:12

And those seeking my soul lay a snare, And those seeking my evil Have spoken mischievous things, And they do deceits meditate all the day.

Psalm 52:1-4

To the Overseer. -- An instruction, by David, in the coming in of Doeg the Edomite, and he declareth to Saul, and saith to him, 'David came in unto the house of Ahimelech.' What, boasteth thou in evil, O mighty one? The kindness of God is all the day.

Psalm 55:21

Sweeter than honey hath been his mouth, And his heart is war! Softer have been his words than oil, And they are drawn swords.

Psalm 59:12

The sin of their mouth is a word of their lips, And they are captured in their pride, And from the curse and lying they recount.

Psalm 62:4

Only -- from his excellency They have consulted to drive away, They enjoy a lie, with their mouth they bless, And with their heart revile. Selah.

Psalm 144:11

Free me, and deliver me From the hand of sons of a stranger, Because their mouth hath spoken vanity, And their right hand is a right hand of falsehood,

Proverbs 20:19

A revealer of secret counsels is the busybody, And for a deceiver with his lips make not thyself surety.

Proverbs 29:5

A man taking a portion above his neighbour, Spreadeth a net for his own steps.

Jeremiah 9:2-6

Who doth give me in a wilderness A lodging-place of travellers? And I leave my people, and go from them, For all of them are adulterers, An assembly of treacherous ones.

Ezekiel 12:24

For there is no more any vain vision, and flattering divination, In the midst of the house of Israel.

1 Thessalonians 2:5

for at no time did we come with speech of flattery, (as ye have known,) nor in a pretext for covetousness, (God is witness!)

Treasury of Scripture Knowledge

Summary

They speak vanity every one with his neighbour: with flattering lips and with a double heart do they speak.

A double heart

Bible References

Flattering

Psalm 5:9
For there is no stability in their mouth. Their heart is mischiefs, An open grave is their throat, Their tongue they make smooth.
Psalm 28:3
Draw me not with the wicked, And with workers of iniquity, Speaking peace with their neighbours, And evil in their heart.
Psalm 62:4
Only -- from his excellency They have consulted to drive away, They enjoy a lie, with their mouth they bless, And with their heart revile. Selah.
Proverbs 20:19
A revealer of secret counsels is the busybody, And for a deceiver with his lips make not thyself surety.
Proverbs 29:5
A man taking a portion above his neighbour, Spreadeth a net for his own steps.
Ezekiel 12:24
For there is no more any vain vision, and flattering divination, In the midst of the house of Israel.
Romans 16:18
for such our Lord Jesus Christ do not serve, but their own belly; and through the good word and fair speech they deceive the hearts of the harmless,
1 Thessalonians 2:5
for at no time did we come with speech of flattery, (as ye have known,) nor in a pretext for covetousness, (God is witness!)

A double heart

1 Chronicles 12:33
Of Zebulun, going forth to the host, arranging battle with all instruments of battle, are fifty thousand, and keeping rank without a double heart.

General references

Genesis 29:19
and Laban saith, 'It is better for me to give her to thee than to give her to another man; dwell with me;'
Judges 16:6
And Delilah saith unto Samson, 'Declare, I pray thee, to me, wherein thy great power is, and wherewith thou art bound, to afflict thee.'
Habakkuk 1:3
Why dost Thou shew me iniquity, And perversity dost cause to behold? And spoiling and violence are before me, And there is strife, and contention doth lift itself up,
Acts 12:22
and the populace were shouting, 'The voice of a god, and not of a man;'