The two-edged sword
For the word of God is quick, and powerful, and sharper than any twoedged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart. (Hebrews 4:12 KJV)
Thus says the New Testament book of Hebrews, but why should we be considering it here? It is because the same phrase crops up in this Psalm:
Let the saints be joyful in glory: let them sing aloud upon their beds. Let the high praises of God be in their mouth, and a twoedged sword in their hand; To execute vengeance upon the heathen, and punishments upon the people; To bind their kings with chains, and their nobles with fetters of iron; To execute upon them the judgment written: this honour have all his saints. Praise ye the LORD. (Psalm 149:5-9 KJV)
The word of God, when embodied in a person who understands and knows it, will pronounce righteous judgement. This is what Hebrews says. It is because the word is able to discern the hidden “thoughts and intents of the heart”, because that’s how God has designed it.
But it only works for our own heart, and our own intentions. We cannot use this sword on anyone else than ourselves. This self examination is the subject of that chapter in Hebrews where we get the reference to the two-edged sword.
So, since the word of God is consistent, this must also be what the sword is in our Psalm — not a physical sword — but the ability of the word of God to discern the thoughts and intents of the heart.
It therefore stands to reason that what the Psalm is actually talking about is the saints of God being given the ability to look into the hearts of others and to discern the thoughts and intentions they see there. If this prophecy is speaking of the Kingdom age, it means that there will be no place to hide for those who continue to hate the Lord Jesus, and despise the righteous laws he instigates.
But there is a reason to believe that the Psalm isn’t talking about the Kingdom age, but just before. Look at this passage again and see if you notice anything odd:
Let the saints be joyful in glory: let them sing aloud upon their beds. Let the high praises of God be in their mouth, and a twoedged sword in their hand; (Psalm 149:5-6 KJV)
Did you spot the reference to the saints in their beds? Well, in the Kingdom age, saints will have no need for beds, for:
For when they shall rise from the dead, they neither marry, nor are given in marriage; but are as the angels which are in heaven. (Mark 12:25 KJV)
So this Psalm may be speaking of a time before the Kingdom, when the Saints, for whatever reason, are given the responsibility for triggering the judgements on the world that have been so long prophesied.
Whether or not that is the case, it seems from other prophecies that this judgement role will certainly be there in the Kingdom age:
Do ye not know that the saints shall judge the world? and if the world shall be judged by you, are ye unworthy to judge the smallest matters? (1 Corinthians 6:2 KJV)