Exodus 30:15
The rich shall not give more, and the poor shall not give less than half a shekel, when they give an offering unto the LORD, to make an atonement for your souls. The rich shall not give more, and the poor shall not give less than half a shekel, when they give an offering unto the LORD, to make an atonement for your souls.
Every person counted was to pay exactly half a shekel, with the rich forbidden to give more and the poor forbidden to give less. This was a yearly payment required from every Jew. It stood as a ransom for his soul, atonement money for the lives of the people.
The money thus gathered funded the service, upkeep, and support of the tabernacle and the temple. This required collection was distinct from the large freewill offerings placed in the temple treasury. It had to be paid in the sanctuary coin called the temple shekel, so all foreign money had to be exchanged for it.