The Law of First Mention, also called the Principal of First Mention, simply means that the first time an important word or phrase is used in the Bible it is in its most understandable or simplest form. As it continues to be referred to, that concept is expanded upon and more fully developed.
Genesis, the book of beginnings, contains many of the “First Mentions,” like: God, heaven, good, atonement, covenant, family, sacrifice, love, salvation and many, many more.
You can use a tool like eSword, available for free download at e-sword.net, or the Blue Letter Bible at blueletterbible.org, to look up a word or phrase to find its First Mention, and all the other verses with the same word or phrase. This way you can see how the concept develops.
Let’s take the word “blood” and extract its first mention and a few random verses.
Genesis 4:10
And he said, What hast thou done? the voice of thy brother’s blood crieth unto me from the ground.
Genesis 9:4
But flesh with the life thereof, which is the blood thereof, shall ye not eat.
John 6:53
Then Jesus said unto them, Verily, verily, I say unto you, Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you.
Ephesians 2:3
But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ.
Hebrews 12:24
And to Jesus the mediator of the new covenant, and to the blood of sprinkling, that speaketh better things than that of Abel.
1 John 1:7
But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.
Revelation 19:13
And he was clothed with a vesture dipped in blood: and his name is called The Word of God.
In just seven verses we can see how the word “blood” is expanded upon throughout the Bible. With an extended study we will learn much more about this complex word and concept.
Understand that the Law of First Mention is better termed the Principal of First Mention as it is intended to be a guideline, and concepts must be taken in context.
Applying this principal is a powerful and simple way for us to greatly expand our knowledge of Biblical concepts.