Chassidus differentiates between two general categories of the physical: gashmiyus—“physicality” and chumriyus—“coarseness.” The term gashmiyus refers to something that is physical, but not animalistic or coarse per se. To be sure, everything physical conceals the absolute reality of Hashem, and even the higher spiritual worlds, and is undesirable in that sense. However, gashmiyus refers to physicality of a kind that does not actively entice one to sin or otherwise behave inappropriately in any way. For instance, an ordinary table is a physical, mundane item; although it conceals the divine life force that sustains it; however, it contains no further inappropriate element.
Then there is chumriyus, which is coarse gashmiyus. This refers not only to worldly objects related to sin (which are obviously coarse), but also to objects that have some kind of inappropriate or crass element that is liable to desensitize the person and bring one to decline spiritually until he or she ultimately falls into sin.
Of this, our sages teach: “Such are the wiles of the evil inclination: Today he says to him, ‘Do this’; tomorrow he tells him, ‘Do that,’ until he tells him, ‘Go and serve idols,’ and he goes and serves [them].”
The challenge of gashmiyus is to fulfill the Torah’s instructions, “All your actions should be for the sake of Heaven,” and “In all your ways, know Him.” Not only should gashmiyus not be used for sin, G–d forbid, but it should not even be used for personal benefit alone. Rather, all one’s gashmiyus should be used to serve Hashem, and only then does one rectify it and elevate it.
In contrast, one should in general abstain from chumriyus, and in that way one rectifies it.
As mentioned, Tefillah is “a ladder fixed in the earth” whose “head reaches the heavens.” “Earth—aretz” refers specifically to gashmiyus, not chumriyus. Thus, part of Tefillah is rejecting chumriyus from our lives.
Then Tefillah acts as a two-way ladder connecting the “earth,” the gashmiyus, with “the heavens,” the spiritual. It functions “from below to above,” by elevating the physical to the spiritual, and “from above to below,” by bringing the spiritual down into the physical.
Based on Likkutei Dibburim, Vol. 3, p. 497.
 Shabbos 105b.
 See Kuntres Uma’ayan, p. 66.
 Avos 2:12.
 Mishlei 3:6.
 Cf. Tanya ch. 6.