Westminster Shorter Catechism Q. 35, Of Sanctification, sits directly behind the sermon's opening movement. Boaz intends to redeem not only Ruth's circumstances but her whole self, physical, emotional, reputational, and spiritual. The catechism captures exactly this: sanctification is the work of God's free grace, whereby we are renewed in the whole man after the image of God, and are enabled more and more to die unto sin and live unto righteousness. Christ, the greater Boaz, does not stop at legal acquittal. He transforms everything.
WCF Chapter 5, Of Providence, provides the doctrinal backbone for the sermon's application on waiting. The confession affirms that God the great Creator of all things does uphold, direct, dispose, and govern all creatures, actions, and things, from the greatest even to the least, by his most holy providence. Nothing in Ruth's situation, not the unanswered question of the nearer redeemer, not the uncertainty of the morning, not the waiting that follows, is outside the governing hand of a Father who is good. His sovereignty would be terrifying if he were not also good, and the cross is the permanent evidence that he is both.
WCF Chapter 11, Of Justification, and Chapter 13, Of Sanctification, together frame what the six measures of barley picture: God does not merely declare us righteous and leave us where we are. He begins a work of transformation that he will not abandon until it is complete. The pledge is given. The marriage is certain. The Redeemer will not rest until every requirement is satisfied and the bride is brought home.