Isaiah 54:17 (KJV) says:

No weapon that is formed against thee shall prosper; and every tongue that shall rise against thee in judgment thou shalt condemn. This is the heritage of the servants of the Lord, and their righteousness is of me, saith the Lord.

This scripture does not say that no weapon would be formed against you. Instead it says that when it is formed against you, it will not prosper.  So, don't sweat it when someone attacks you, whether by words or actions, because it won't prosper. 

Often words will not have a lasting effect if we refuse to take offense or get hurt by them.  When someone says something against you, just get alone and say, "I condemn those words.  They have no effect on me or my life."  Begin to confess that you're too blessed to be cursed, and that God turns curses into blessings for you.

According to this scripture in Isaiah, this is our heritage, or our right as children of God.  We overcome evil with good.  We'll say what God says about our situation.  We can make statements like, "God is working this out for my good.and in my favor."

The word righteousness in this verse actually means vindication.  God will make things right.  We don't have to defend ourselves.  The battle is the Lord's.

In the New International Version (NIV), Isaiah 54:17 says:

No weapon forged against you will prevail, and you will refute every tongue that accuses you. This is the heritage of the servants of the Lord, and this is their vindication from me,” declares the Lord.

This applies to any number of situations that we can find ourselves in: court cases, family relationships, workplace conflict, etc.

I remember a situation in which people where I worked were coming against me.  I felt attacked, criticized, and isolated.  I must be honest and say that, like most believers, I haven't always used the wisdom of God in every workplace scenario.  However, in this situation I held onto this word from Isaiah and I spoke the word over my situation and my co-workers. After a period of time, I began to see a change.  God vindicated me and gave me favor, silencing the voice of the enemy.  He gave me the victory.

So, don't forget, as we speak God's Word and praise Him, our enemies will be silenced and we will be avenged.

Psalms 8:2 (NIV):

Through the praise of children and infants you have established a stronghold against your enemies, to silence the foe and the avenger.

Psalms 149:6-9 (Common English Bible, CEB):

Let the high praises of God be in their mouths and a double-edged sword in their hands, to get revenge against the nations and punishment on the peoples, binding their rulers in chains and their officials in iron shackles, achieving the justice written against them.  That will be an honor for all God’s faithful people.  Praise the Lord!

I Corinthians 15:57 (KJV)

But thanks be to God, which giveth us the victory through our Lord Jesus Christ.