A Science Teacher Looks at Hebrews 9

Updated: Mar 5


When I was a kid I remember reading these verses and being really puzzled by the idea that blood could clean. My only experience was otherwise. Blood soiled things. It stained. It festered. How could this thick liquid wash me? Such were the musings of a concrete thinker.


  • Under the old system, the blood of goats and bulls and the ashes of a heifer could cleanse people's bodies from ceremonial impurity. Hebrews 9:13


It wasn’t until I considered blood on a biological level that the analogy began to make sense. Blood is the main purifying agent of our body. It is the great detoxifier.


Without blood flow we’d be dead—fairly fast. As a swimmer I was puzzled by the idea that someone needed mouth to mouth immediately after a heart attack. After all, I reasoned, I can hold my breath for well over a minute. The world record is in the range of a quarter hour. So why can’t someone survive for longer?


...for the life of the body is in its blood. Lev 17:11


It never dawned on me until much later that it wasn’t the breathing, but the blood flow. When your heart stops so does circulation. And stopping blood flow, even locally, can be catastrophic. It goes by different names depending on the location—stroke, pulmonary embolism, heart attack, muscle infarction— but the results are always serious.


  • For by the power of the eternal Spirit, Christ offered himself to God as a perfect sacrifice for our sins. Hebrews 9:15b

Blood has many jobs. Should you wish to study any of them you could spend an entire career without exhausting the subject.


As I outline a few, think again about the words from Hebrews 9 and see them in a new light.


  • Blood wages war against disease. We’re bombarded by microbes, viruses, and bacteria but most never get through our defenses. White blood cells eat them for breakfast... literally. Before the pathogens can reproduce and wreak havoc, they’re toast.

  • Blood responds to injury. When we’re cut or bruised, inside or out, it’s our blood that takes action. Platelets move into the site to form clots and prevent blood loss. They also recruit the white blood cells to take action. These cells clear the debris and begin tissue repair. They absorb the damaged cells and secrete a matrix which will provide the scaffolding for new tissue to grow. Cool.

  • Blood removes impurities. Every cell in our body respires—using oxygen and producing wastes CO2 and urea. Blood picks up the waste and drops it in the lungs and kidneys respectively where the body excretes it.

  • Blood brings sustenance. Every cells in our body respires—they use oxygen to release the energy stored in food. Red blood cells carry the oxygen to all of our cells so they can get the energy to do their jobs.

  • Blood transports hormones. Hormones are signaling molecules. They’re made in glands and regulate all types of physiology and behavior. We couldn’t live without them.


For patients in need of blood transfusions, there is no substitute. When patients receive blood, their color returns, their energy improves and their heart rate calms. Millions of people donate blood each year. It’s a selfless gift. Neither the giver nor receiver will ever know each other. Yet the gift matters. Significantly.


Blood transfusions are an intricate business. Human blood transfusions began in the early 20th century but were very risky since the complications were still unknown. Today they save many millions of lives each year.


There’s another blood transfusion that can heal us. Two thousand years ago, Christ, the perfect donor, hung on a cross. He shed his blood so that we could live… really live, free and forgiven, our complete brokenness made whole. We change because of the life in that blood.


Do you study blood and circulation in your science class? What activities do you use to help kids understand its various jobs? We have a few different ones including a game that helps kids understand blood circulation and what happens where. You can find it and all of the teaching labs inside the Engaging Science Labs Collection membership.

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