Theseus is made up of "these" and "us", which are both definite pronouns, i.e. they state precisely what they are referring to. "Indiscriminately" implies "vaguely; imprecisely", So, "not...indiscriminately" means "not vaguely; not in an imprecise manner", hence, "These" and "us", namely, these (not them) and us (not just anybody).