Explain and show how these lines are relevant in the text in terms of its central theme and structure.
"Will ye see how they swaddle
His four feet in the middle?
Saw I never in a cradle
A horned lad ere now. "
"The Second Shepherd's Play" (Secundum Pastorum), part of the Wakefield Cycle (ca. mid-15thC), is the most well-known English drama of the medieval era and serves two purposes. It is, first, a satire on medieval nativity plays--the first half concerns Mak and Jill's stealing of a sheep and pawning it off as the Christ child, worshipped by the three shepherd's until they discover Mak and Jill's ruse. The second half comprises a conventional medieval nativity play in which the common folk of rural England are introduced to Christ, who brings them peace and the hope of a better world.
The quote you propose as integral to play's structure and theme is important because, among other things, it serves as the catalyst for the transition from the slapstick, silly first half of the play in which the shepherd's lose a sheep to Mak, who then converts the sheep into the Christ child in order to disguise his theft. Even though the first half is meant to be satire, every listener would understand the symbolism of the stolen sheep, which represents Christ and therefore plays a dual role in the first half.
This discovery of the fraud, however, aside from allowing the play to transition from satire to serious nativity celebration, is very important for another reason. Sheep stealing was a serious crime, often punishable by death, and it would have been within the shepherd's rights to punish Mak and Jill severely. Instead, after noting that the child has four hooves and a "horned" head, they punish Mak by tossing him playfully--and harmlessly--in a blanket. In other words, their feelings of good will--although created by a false Christ child in the form of their own sheep--overrides their aggressive impulse to punish Mak severely. The symbol, in this case, is as powerful as the real Christ.
The influence of the "Christ" child, even if just a sheep, has profoundly effected the shepherds, who are only interested in exacting a painless vengeance on Mak, and the second half of the play is almost anti-climactic in that the important business--the forgiveness of Mak--has already taken place.