The Israelites were instructed to mark the doorposts of their homes with the blood of a slaughtered spring lamb. Upon seeing this, the angel of the Lord knew to pass over (as in not kill) the first-born in these Jewish homes, hence the name of the holiday: Passover.
Passover is an important religious observation for ancient (and modern day) Jews. During Jesus's lifetime failure to visit the Temple (in Jerusalem) and deliver an offering during Passover was one of thirty-six transgressions that would result in the holy punishment of karet, or being spiritually “cut off” from God.
Hundreds of thousands of Jewish believers traveled great distances (mostly on foot) —from Galilee, Syria, Egypt, and even further — to celebrate the climax to the Jewish religious year, every year, during this period of history.
To atone for their sins, pilgrims were required to purchase a lamb (or dove) for sacrifice on the Holy Altar, as well as pay the "Temple Tax" using a special coin called a Shekel. In keeping with the Jewish law forbidding graven images, these coins were decorated with images of plants and other nonhuman likenesses.
A lucrative trade developed that sold Shekels and animals to the pilgrims. Many vendors (and priests) lavishly lined their own pockets taking advantage of (and frequently cheating) the faithful by charging unfair prices for these items.
Jesus, during his annual pilgrimage to the Temple, would violently confront this practice -- and hence become the topic of much conversation among the crowd around Jerusalem during April of 27AD.
