What does it mean to be made in the image of God?

It means God stamped something onto humans that he stamped onto nothing else he made.

The Hebrew word is צֶלֶם (tselem, "image") — and its primary meaning in the Old Testament is physical representation. Elsewhere in the Hebrew Bible it describes idols: a carved likeness made to resemble something real. When Genesis 1:26–27 applies this word to the human, it says that humans bear a representational correspondence to God himself that no animal, no plant, and no angel carries.

"And God said, 'Let us make humankind in our image, according to our likeness.'" — Genesis 1:26

"And God created the human in his own image; in the image of God he created him; male and female he created them." — Genesis 1:27

That last verse is striking for its repetition — the word "image" (tselem, H6754) appears twice in a single verse, more densely than almost anywhere else in the Hebrew Bible. The narrator is not being redundant. He is insisting.

The image turns out to be a thread that runs through the whole canon.

In Genesis 5:3, Adam fathers Seth "in his own likeness, according to his image" — the two terms (demut and tselem) appear in reverse order from Genesis 1:26, a mirroring that seals creation and procreation together. What God pressed into Adam, Adam transmits to Seth. The image is heritable through human biology.

In Genesis 9:6, after the flood, the image becomes the legal foundation for the prohibition on murder:

"Whoever sheds the blood of a human, by a human shall his blood be shed; for in the image of God he made humankind." — Genesis 9:6

The word for (כִּי, ki) makes the structure explicit: the image is the premise; the death penalty for murder is the conclusion. Killing a person is an assault on the divine image embedded in that person. The image survives the flood and the judgment unchanged.

James picks up the same logic for speech: "With [the tongue] we curse humans who are made according to the likeness of God" (James 3:9) — using the Greek word for "likeness" (ὁμοίωσις, G3669) that the Greek Old Testament used to translate the Hebrew demut (H1823). Cursing a person curses an image-bearer.

The thread reaches its destination in the New Testament, where εἰκών (eikōn, G1504) — the Greek word the Septuagint used to translate tselem — is applied to Christ: "who is the image of the invisible God" (Colossians 1:15; 2 Corinthians 4:4). The image humanity was created to bear turns out to have been reaching toward its fullest expression all along. And the goal of redemption is described in those same terms: "conformed to the image of his Son" (Romans 8:29); "renewed according to the image of the one who created him" (Colossians 3:10).

The image that was placed at creation, transmitted through procreation, grounded in law, and fractured at the fall — is being restored through conformity to the one who is the image of God in his very nature. First Corinthians 15:49 calls this the exchange of the earthly image for the heavenly one. The thread that began in Genesis 1:26 closes in the resurrection.

The full study After Their Kind traces this chain verse by verse — and shows why the fact that the "kind" vocabulary was withheld from humans in Genesis 1 is what makes the image-language so significant.