In the New Testament, What is the Origin of “Believe In” and “Believe Into”?

Question

Is there any Extra-Biblical source, (in Classical Greek, or Semitic sources), or a syntactical rule, behind the construction: ["πιστεύων ἐν" and "πιστεύων εἰς" + "Some Leader"]* — Or, is this phenomena unique to New Testament texts?

John 3:16, NASB - 16 “For God so loved the world, that He gave His only begotten Son, that whoever believes in Him [πιστεύων εἰς αὐτὸν] shall not perish, but have eternal life.

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Notes:

The argument, that this construction forms figures-of-speech, (Metonymy, etc), in the form [Verb + ἐν or εἰς + "Some Leader"], seems to be supported by the repetitive use of two specific forms in the New Testament, ("Believe In/Into", and "Baptized Into") :

Romans 6:3, NASB - Or do you not know that all of us who have been baptized into Christ Jesus [ἐβαπτίσθημεν εἰς Χριστὸν Ἰησοῦν] have been baptized into His death [εἰς τὸν θάνατον αὐτοῦ ἐβαπτίσθημεν]?

1. πιστεύω is understood to mean "Trust".
2. New Testament use is complicated, by a lack of apparent use in Classical Greek.
3. The New Testament appears to distinguish the use of the Greek word, "to Trust/Believe", from another, which takes a preposition, coupled with "Into/εἰς".

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Other Similar Questions

The Source/Precedent issue is distinct from issues raised in other questions:

1. The word 'believe' in John 3:15-16; (which is admittedly very close), but pursues the dichotomy of believing "about Jesus", or "believing what he said."
2. What is the difference between πιστεύων ἐν αὐτῷ and πιστεύων εἰς αὐτὸν? appears to be a survey, and juxtaposes "πιστεύων ἐν αὐτῷ" and "πιστεύων εἰς αὐτὸν",

Answer 1

I will answer your “Question 1”, as this is not addressed in the earlier question.

In Classical Greek πιστεύω means “trust, put faith in, rely on” and takes an object in the dative or accusative; it is never (as far as I can see) construed with the prepositions ἐν or εἰς. This construction is, however, commonplace in LXX and NT, e.g. Ps. 77:22, where ὅτι οὐκ ἐπίστευσαν ἐν τῷ θεῷ translates כִּי לֹא הֶאֱמִינוּ בֵּאלֹהִים quite literally (with ἐν for the preposition b-), "because they believed not in God" (KJV Ps. 78:22). I would think that this usage is a Semitism in Jewish koine.

Similarly Latin “credo” never takes the preposition “in” in the classical language, but “credo in + accusative” is commonplace in ecclesiastical Latin.