Much as Rubens admired (and to some extent sought to emulate) the earl’s impressive accomplishments as a collector and humanist, he chose to represent Arundel as a warrior, in armor, wearing the Order of the Garter, and holding the gold baton symbolic of his role as Earl Marshal of England. In this hereditary post, Arundel presided over the country’s nobility and upheld its traditions of chivalric honor. Rubens’s imposing likeness conveys not only the pomp and ceremony associated with this office, but also the earl’s innate reserve and haughty demeanor.
Source: Marjorie E. Wieseman, "Portrait of Thomas Howard, 2nd Earl of Arundel," in Eye of the Beholder, edited by Alan Chong et al. (Boston: ISGM and Beacon Press, 2003): 139