We are instructed by the apostle Paul to wield the sword of the Spirit:
17 Take the helmet of salvation and the sword of the Spirit, which is the word of God.
Ephesians 6:17
What does the Bible teach us about the sword of the Spirit?
The sword belongs to the Holy Spirit.
In Revelation 2:12 we see that the Holy Spirit has the sword:
12 “To the angel of the church in Pergamum write:
These are the words of him who has the sharp, double-edged sword.
Revelation 2:12
The Holy Spirit fights with the sword:
The Holy Spirit speaking in Revelation 2:16 says:
16 Repent therefore! Otherwise, I will soon come to you and will fight against them with the sword of my mouth.
17 Whoever has ears, let them hear what the Spirit says to the churches.
Revelation 2:16-17a
Clearly, using the sword involves fighting with the mouth. In Isaiah 49:2a the Holy Spirit says:
2 He made my mouth like a sharpened sword,
Isaiah 49:2a
What does it mean that the Holy Spirit has a mouth like a sword and that He uses this sword to fight? How exactly does He use His mouth as a sharpened sword?
The best example occurred at the temptation of Jesus when He used scriptures to fight against the temptations and erroneous misinterpretation of scripture that the devil uses to fight against Him.
4 Then Jesus was led by the Spirit into the wilderness to be tempted[a] by the devil. 2 After fasting forty days and forty nights, he was hungry. 3 The tempter came to him and said, “If you are the Son of God, tell these stones to become bread.”
4 Jesus answered, “It is written: ‘Man shall not live on bread alone, but on every word that comes from the mouth of God.’[b]”
5 Then the devil took him to the holy city and had him stand on the highest point of the temple. 6 “If you are the Son of God,” he said, “throw yourself down. For it is written:
“‘He will command his angels concerning you,
and they will lift you up in their hands,
so that you will not strike your foot against a stone.’[c]”7 Jesus answered him, “It is also written: ‘Do not put the Lord your God to the test.’[d]”
8 Again, the devil took him to a very high mountain and showed him all the kingdoms of the world and their splendor. 9 “All this I will give you,” he said, “if you will bow down and worship me.”
10 Jesus said to him, “Away from me, Satan! For it is written: ‘Worship the Lord your God, and serve him only.’[e]”
11 Then the devil left him, and angels came and attended him.
Matthew 4:1-11
In the above verses we see how Jesus sliced through all of the temptations of Satan with scriptures which effectively negated and destroyed every lie and temptation that Satan used against Him.
In Ephesians 6:17 the apostle Paul is urging the church to use the scriptures as a weapon against Satan in the same way as they are used by Jesus, the incarnate Holy Spirit, to defeat Satan in Matthew 4.
The scriptures are His sword and He is familiar with how to use them to fight the enemy. Clearly to use the sword of the spirit effectively, we must know the scriptures thoroughly, as He did, and we must allow Him to guide us when it comes to knowing how to wield them.
For further information regarding the relationship between the Holy Spirit and the Word of God see the following article by James Rosenquist: The Connection between the Holy Spirit and the Word of God.