psalm 109 David writes this psalm.  He does not hold back from praying against the wicked men who have come against him. He has no plea for mercy for those who have harmed him.  These are bold words.  These people were wicked and deceitful.  They lied.  They spewed out words of hatred. They falsely accused him.  They were evil towards him.
This is what David prays for The Lord to do to them:
Let someone accuse them of something, and let the judge find them guilty.
Let their prayers be a sin.
Let his position be usurped.
Let his children be fatherless.
Let his wife be a widow. ( In other words, let him die.)
Let his children be left in poverty and homeless.
Let all that he left behind be taken by creditors and strangers.
Don't let anyone show him or his children mercy.
Let his whole family be blotted out. Cut off.  Condemned forever.
This is David's prayer! 
But he goes on to tell us more about the wicked man.   The man who never showed lovingkindness.
He persecuted the afflicted and needy.
He killed the sad of heart.
He loved to curse and hated to bless others.
Cursing others was so much a part of who he was that it was like a robe that covered him, water that entered him, and oil inside his bones.  This adversary has the character of the evil one.  He is a child of Satan himself.  No wonder David prays for him to be wiped out. This is one "of those who speak evil against my soul" ( v20).  The accuser, Satan, does this against us who believe in God.
Verse 21 is a turning point in David's prayer.  He has made his case against the enemy, and now he makes his petitions to The Lord.
"But Thou, O God, The Lord, deal kindly with me for Thy name's sake; Because Thy lovingkindness is good, deliver me."  David has suffered from this persecution.  He calls himself afflicted, needy, wounded, shaken off, weak, humiliated.  But his hope is in The Lord Who saves, Who shows mercy,  Who helps the needy, Who judges the wicked.
David ends with thanksgiving and praise to God. Everything is in His Hands.  So thankful this is true.  David's enemies are like ours - his struggles the same "schemes of the devil" that we face. Eph. 6:12 tells us "For our struggle is not against flesh and blood, but against the rulers, against the powers, against the world forces of this darkness, against the spiritual forces of wickedness in the heavenly places."  David took up the "full armor of God", the same armor available to us:
Truth - God is good!
Righteousness- God delivers those Who love Him, but He judges the wicked and will destroy them.
Gospel of peace - We have been brought into relationship with God through Christ, He has delivered us.
Faith - We trust God to deal with the wicked and we trust Him alone to help us in our need.
Salvation - He alone can save us.
The Word of God - It is a sword of the Spirit, we take it up as David did against the enemy.
Prayer- David prayed in every circumstance and we must too.

Revelation 2:12-17 The 3rd letter.  Jesus calls Himself "the One who has the sharp two edged sword".
The Word. The sword of the Spirit.  These people lived "where Satan's throne is" and "where Satan dwells".   They lived where the faithful were killed.  They held fast to Christ and to faith.  The problem they had wasn't from this enemy outside of the church, but came from inside. Some were teaching false doctrines  which were leading to sinful living.  Jesus calls them to repent.  He says He will "make war against them with the sword of " His mouth.  But to the overcomer Jesus promises hidden manna and a white stone with a new name.

It is never a coincidence when a common theme is presented in two passages.  There is indeed an attack of the enemy underway in my family.  I thank You Father for the Word of God, the sword of the Spirit and I take it up.  Your Word is True and I stand on Your promises.  I believe in Your lovingkindness and ask for Your help for the afflicted and needy. Deal kindly with them O Lord.
"With my mouth I will give thanks abundantly to The Lord"