When an item needs to be redeemed or bought back because it was lost or sold a price must be paid for its return. We were lost to sin and Jesus paid the ransom for us with his blood, his blood was the measure of redeeming grace being the measure of God's own eternal goodness to each of us. It was by the foolishness of preaching the gospel that we were reconciled back to God. Our reconciliation afforded us the salvation of Christ in perfect wisdom and prudence. Wisdom is that which make men judge what are the best ends and the best means to attain them to give men council and direction.
Prudence is wisdom applied to practice.
The gospel is God's perfect wisdom and prudence applied to man. The Call of Both Jews and Gentiles . The mystery was that the Gentiles should ever be received into the Church of God not having any ceremonial rites of the law. This mystery of God's will was revealed to the apostles and they went about preaching the gospel to every creature whether Jew or Gentile, bond or free. This all came to be according to the good pleasure of God.