The goad is a traditional farming implement, used to spur or guide livestock, usually oxen, which are pulling a plow or a cart; used also to round up cattle.
In Judges 3:31, the shophet Shamgar, son of Anath, kills six hundred Philistines with an ox goad.
The image of prodding the reluctant or lazy creature made this a useful metaphor for sharp urgings, such as the prick of conscience, the nagging of a mate, or the "words of the wise," which are "firmly embedded nails" in human minds (Ecclesiastes 12:11-12).
Lamed means 'goad' and in particular an ox-goad, as if we use the power of Gevurah to goad that Aleph ox, the silent letter, into a more tangible physical existence in the heart of the tree [of life].
Lamed begins the Hebrew words for both "learn" and "teach," and so encompasses the most Kabbalist of activities, study.