Does "stand" have the meaning of "be helpful for"?

"something stands somebody in good stead" is a common idiom, which means "something is helpful for somebody in the present and future".

However, under the entry "stand" in the OXFORD dictionary, there is no meaning item equivalent to "be helpful for".

Is there any explanation for "stand"'s meaning in the idiom?

The verb to stand is one of the oldest verbs we have in English, dating from 825 ᴀᴅ. The OED gives 350 different senses for this verb, 140 main senses and 210 subsenses. This one isn’t really anything too special.

The particular use you ask about is documented in subsense b of sense 48. This exact sense of the verb stand in conjunction with stead dates from around 1300 ᴀᴅ, appearing first in the written record as the Middle English of Cursor Mundi.

IV. Phrases and idiomatic uses.

48. to stand in stead v.

    • †a. To be of use or advantage, to be serviceable or profitable. Also with adjective qualifying stead, to be of (little, no, good) avail or service. Obsolete.
    • b. More usually with indirect obj. (†rarely with to). to stand (one) in (good, etc.) stead: to be of service or benefit to; to help or avail. Now only with adj. (good, etc.), and that in literary rather than familiar use.
      
      ^{When without epithet, in stead was sometimes written or printed as one word.}
    • †c. Similarly to stand (one) to (good) stead. Also without preposition, to stand (one) stead. Obsolete. rare.
    • †d. In various other phrases of like meaning, as to stand (a person) in force, in profit, in vail, at or to avail. to stand (in) stall: see ꜱᴛᴀʟʟ n.¹ 2b. Obsolete.

Notice how they mention that this phrase now occurs mainly in “literary” use rather than in “familiar” use. Here are a few of the older citations they provide for subsense 48b:

• 1387 J. Trevisa tr. R. Higden Polychron. (Rolls) VII. 267
  But for it stood hem but litel in stede [L. sed quia parum profecerunt].
• 1665 in Extracts State Papers (Friends’ Hist. Soc.) (1912) 3rd Ser. 241
  Our good intentions stand us in little stead.
• 1749 H. Fielding Tom Jones II. v. viii. 182
  It is then he will find in what mighty Stead that Heathen Goddess..will stand him.
• 1848 Thackeray Vanity Fair liv. 487 A Johnson's Dictionary, which stood them in much stead.
• 1887 W. Westall tr. ‘A. Laurie’ Capt. Trafalgar i. 13
  Continual practice stood me in better stead than whole volumes of theory.
• 1891 Temple Bar Oct. 177
  His early training..stood him in good stead.

Those all have a personal pronoun as a benefactive indirect object. That’s because one stands someone that way, so that is the person who benefits from the standing.