Thou shalt not covet thy neighbor's wife; thou shalt not covet thy neighbor's house; nor his field, nor his servant, nor his maid, nor his ox, nor his ass, not any of his cattle, nor whatever belongs to thy neighbor.
The Tenth Commandment (Septuagint)
There is no other passion engendered in human souls more pernicious than envy. It does less harm to strangers, but is the chief homegrown evil for whomever possesses it. As rust eats away at iron, so envy eats away at the soul in which it lives. To say it better just as they say of vipers, that they are born by gnawing through the belly that gives them birth, so also envy usually devours the soul which is tormented by it. Envy is grief over a neighbor's wellbeing. Therefore, the envious man never has a lack of sorrows and afflictions. What can be more pernicious than this disease? This is a corruption of life, a profanation of nature, enmity against what is given to us by God, opposition to God.
Saint Basil the Great
Whoever thou might be, O envious and malicious one, look at how wicked thou art with regard to those whom thou hatest, how noxious and unpleasant. Thou art the enemy of no one else but thine own salvation. Everyone whom thou persuest with envy can run and slip away from thee, but thou canst not run away from thyself. Wherever thou might be, thine adversary is with thee, the enemy is always in thy heart, perdition is contained within. Thou art entangled in and bound by unbreakable chains, thou hast become a captive of the jealousy that has prevailed over thee, and no consolation whatever will come to thine aid. The Lord said: "…he that is least among you all, the same shall be great" (Luke 9:48). By His response, He annihilated all jealousy. It is not permitted for a disciple of Christ to be jealous and to envy.
Saint Cyprian of Carthage
And what, tell me, dost thou envy? That thy brother has received a spiritual gift? But from whom did he receive it, tell me; was it not from God? That means that thou art at enmity with Him Who gave to him. Seest thou not to what extent evil extends, to what degree of sin it mounts and what an abyss of punishment it digs. Let us, beloved, flee this passion; let us not begin to envy, but let us pray for the envious and use all measures in order to exterminate this passion in them.
Saint John Chrysostom
Do not envy anyone, O man, for their earthly, passing happiness, for everything in the world is as the grass and the flower of the field; do not envy the rich and the glorious; do not envy those who are surfeited with earthly pleasures; but sensibly imitate him who is adorned with virtues. Do not desire authority, honor, any advantages whatever; do not desire excellent dwellings and buildings, or any other luxury; for all this is temporary and corruptible, all is passing away and quickly will vanish like smoke. Everything will remain here, everything will be turned into dust and ashes, for nothing is eternal on the earth. Only be sensibly zealous for those things which are united with the Lord or are deemed worthy of the grace of the Most Holy Spirit; for whoever receives it will be richer and more glorious that all the rich and glorious.
Saint Demetrius of Rostov