What does פִּיו mean in the modern Hebrew translation of διʼ αὐτοῦ in John 1:7?

Question

What does פִּיו mean in the modern Hebrew translation of διʼ αὐτοῦ in John 1:7?
The ha-Berit ha-ḥadashah translates

ἵνα πάντες πιστεύσωσιν διʼ αὐτοῦ 1

as כְּדֵי שֶׁעַל–פִּיו יַאֲמִינוּ הַכֹּל .

2

The difficult part for me is פִּיו, literally “his mouth,” translating διʼ αὐτοῦ. Looking at passages in BHS (eg. Numbers 27:21), פִּיו appears to mean “his instruction” or “his command.” However in the context “his witness” seems to fit better and the Hebrew translation may be saying “sufficiently that all who believe his witness.” For those who know Hebrew, is this valid?

Note this is investigating how that Hebrew translation interprets John 1:7. It is not the only way to interpret the original Greek.

Delitzsch translated this clause as לְמַעַן יַאֲמִינוּ כֻלָּם עַל־יָדוֹ׃

3

meaning “for the purpose that all (of them) believe through his hand;” leading to how to interpret “his hand.”

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1 Nestle, E., Nestle, E., Aland, B., Aland, K., Karavidopoulos, J., Martini, C. M., & Metzger, B. M. (1993). The Greek New Testament (27th ed., Jn 1:7). Stuttgart: Deutsche Bibelgesellschaft.

2 ha-Berit ha-ḥadashah. (2000). (Jn 1:7). Israel: The Bible Society in Israel.

3 Franz Julius Delitzsch. (n.d.). Delitzsch Hebrew New Testament (Jn 1:7).

Answer 1

עַל-פִּי, literally "on the mouth of", is an idiom for "according to, in accordance with; by". You will also see it in the form לְפִי, literally "to the mouth of".

There is no exact equivalence found in the LXX to compare, but consider where κατά translates עַל-פִּי (e.g., Gen. 43:7; Deut. 17:10,11) and where ἐπί translates עַל-פִּי (e.g., Ex. 34:27; Lev. 27:18; Deut. 17:6).

The closest comparison is in LXX Num 35:30 where διά translates לְפִי.