somebody, person, one's station in life
身 centers on the physical self: a person's body, their individual existence, and by extension their social position or station in life.
(one's) self; oneself; yourself; himself; herself
one's body; one's person
body; physical system; (the) person
one's origin (e.g. city, country, parentage, school)
contents; interior; filling
height (of a person); stature
whole (body); full-length (e.g. portrait)
metamorphosis; disguise; transformation; shapeshifting; morphing
(social) standing; status; position; rank
unmarried; single
near oneself; close to one; familiar
lower half of the body; nether parts
relatives; one's family
sashimi (raw sliced fish, shellfish or crustaceans)
upper half of the body; upper body
mind and body
lifelong; lifetime; for life; life
alone; by oneself; unaccompanied; unaided; single-handed; without one's family
(one's) identity; background; upbringing; birth (and parentage)
other self; alter ego; part of oneself (in someone or something else); representation of oneself
body proportions
one's person
movement (of one's body); moving about; stirring
substitution (for someone else); substitute; stand-in; scapegoat; sacrifice
身 is a pictograph of a human body, originally showing a side view of a person with a protruding belly. The modern form retains the general body shape.
The shape of 身 looks like a standing person with a torso and legs. See it as a simple outline of a body, representing a person and their physical self.
For シン, imagine a person's body as a shiny, new machine: shin -> シン, and the body is the vehicle for one's station in life.