"LORD", or "Lord"?
"The LORD said unto my Lord,
‘Sit at my right hand until I make your enemies your footstool.’ "
If my memory serves me correctly, this Old Testament verse is quoted in New Testament books more than any other. Therefore, we know that it contains some wisdom that is important for us to grasp. We know that in this famous verse, the Father is speaking to His Son because Jesus himself said so (Mt. 22:41-45).
In the Old Testament, when "LORD" is spelled with all capital letters, it refers to Jehovah, but "Lord" (only the "L" is capital) refers to anyone in authority lower than Jehovah. Every time you see "Lord" spelled with all capital letters (not just a capital"L"), the original word there is the word for Jehovah.
In the verse above, the LORD (Jehovah) is speaking to someone whom He especially loves, one who has been made so great by Jehovah that king David calls him his "LORD". In that verse, Jehovah is honoring someone with the greatest honor possible for any creature; that is, the exalted honor of being seated at the right hand of Jehovah in heaven. But no one ever knew who Jehovah was speaking to until the spirit of God was given to man in Acts 2. With the spirit’s coming, the understanding came that Jehovah was speaking to the young man crucified by the Romans at Golgotha: Jesus Christ of Nazareth.
Jehovah’s ancient promise to this mysterious person continued in the next verse to speak of Jesus reigning on earth for a thousand years from Zion (that is, from Jerusalem): "The LORD shall send the rod of your strength out of Zion. Rule in the midst of your enemies!"
Then, Jehovah’s promises to this highly honored person continued in verse 3, as He promised him perpetual youth (eternal life), and then, in one of the most famous verses in the Bible, He promised this blessed man an eternal priesthood. He said, "The LORD has sworn, and will not repent, ‘You are a priest for ever, after the order of Melchizedek.’ "
In the remaining verses of this amazing prophetic Psalm, David speaks no more of what "the Lord" will do and speaks instead of "the Lord". Moved by the Spirit, David said, "The Lord at your right hand will strike through kings in the day of his wrath. He will judge among the heathen; he will fill the places with dead bodies; he will wound the heads over many countries. He will drink of the brook in the way; therefore shall he lift up the head." Here, the singing prophet is speaking of Jehovah’s Son, the Lord Jesus, who will make war on the nations and crush them with terrible power when he returns to "rule with an iron rod" over the earth for a thousand years.
Praise ye the LORD!
(And you can praise the Lord, too, while you’re at it.)