The word "meta" means to occupy two positions. In Herbert's poetry, as well as many other metaphysical poets, applying natural law to abstract thought was a technique used to bring forth more meaning to life on a deeper level. The word "metaphysical" is defined as taking into account time and substance in order to discover in-depth meaning to those concepts as well (see: http://dictionary.reference.com/browse/metaphysical?s=ts)
In Herbert's poem "Life," he compares a posy's life in time, space and substance to his own life as well as to life in general. Making this comparison helps him to understand life and death. Basically, he takes up some flowers and holds them most of the morning. He notices that they wither and die within a short amount of time--by noon. He says that Time gently guided them to their death, but they did what they were supposed to do during their short life span by growing, becoming beautiful and smelling sweet.
Since one of the duties of flowers is to fulfill their potential by smelling sweet, he applies that notion to himself and his quality of life by saying, ". . . if my scent be good, I care not if/ It be as short as yours." Using the imagery of a flower's scent, Herbert applies it to fulfilling his own potential in life whatever that may be. If he can fulfill his purpose in life, then he would not be disappointed to live for only a short period of time.