We circumbulate the Ka'ba because it's the example of Prophet Ibrahim. If Allah has decreed something as an act of worship, it is because it is loved by Him, therefore we perform it hoping to gain His pleasure, reward and Mercy. Even if we don't understand how it gain's His pleasure. If it is in accordance with what He has commanded us - we do it. And their is reward and Mercy (in this life and the hereafter) for those who hear and obey.
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