The parable of the hidden treasure (Matt. 13:44) reveals a secret of the kingdom: a joy so great that a man sells all he has to gain it. But before Christ captivates a heart, sin often has, holding it captive to lesser treasures that only look like joy.
The sermon then turns to the cost God paid to free captivated sinners, seen supremely in the gospel, and asks how a captivated heart is set free – pointing to Christ as the greater treasure worth abandoning everything else to gain.