וַיַּ֞ךְ בְּאַנְשֵׁ֣י בֵֽית־שֶׁ֗מֶשׁ כִּ֤י רָאוּ֙ בַּאֲר֣וֹן יְהוָ֔ה וַיַּ֤ךְ בָּעָם֙ שִׁבְעִ֣ים אִ֔ישׁ חֲמִשִּׁ֥ים אֶ֖לֶף אִ֑ישׁ וַיִּֽתְאַבְּל֣וּ הָעָ֔ם כִּֽי־הִכָּ֧ה יְהוָ֛ה בָּעָ֖ם מַכָּ֥ה גְדוֹלָֽה
Entonces hirió Dios á los de Beth-semes, porque habían mirado en el arca de SEÑOR; hirió en el pueblo cincuenta mil y setenta hombres. Y el pueblo puso luto, porque SEÑOR le había herido de tan gran plaga.
Rabbeinu Bahya
A Midrashic approach: (Pessikta Zutrata) there are three things each of which can serve as instrument of disaster or as instrument of bliss. They are: the staff of Moses, the incense, and the Holy Ark. We have evidence that incense was instrumental in halting disaster from Numbers 17,12: “Aaron put on the incense in the midst of the congregation and made expiation for the people....until the plague was checked.” On the other hand, the same incense (even inside the Sanctuary) brought death upon Nadav and Avihu, the two older sons of Aaron (Leviticus 10,1). The Holy Ark became the cause of death of Uzza and the people of Beit Shemesh as we read in Samuel I 6,19, and it could be a source of blessing (Samuel II 6,11) to Oved Edom Hagitti as we read there: “and the Ark remained in the house of Oved-Edom the Gittite three months, and the Lord blessed Oved-Edom and his whole household.” The staff of Moses which consisted of a material known as sanpiryon, smote the river Nile, brought plagues on the Egyptians. But it also produced water from the rock at Refidim, renamed Massa u-merivah. Thus far the Midrash.
Rashi
Do not look upon me. Do not look upon me disrespectfully, as in, “for they had gazed [disrespectfully] upon the Ark of Adonoy.”23I Shmuel 6:19.
Rashbam
ואל אצילי בני ישראל לא שלח ידו. Even though these people had deliberately lingered over a vision of G’d, feasting their eyes on it, something forbidden as we know from Numbers 4,20, that glimpsing something sacred inside the temple is forbidden on pain of death, at this time G’d did not punish tem. We know of a similar occurrence in Samuel I 6,19 when the subject was the Holy Ark. On the other hand, when afforded a similar opportunity to “see” G’d, Moses was afraid to do so (Exodus 3,6 at the burning bush). Here the nobles and elders were being honoured by G’d with visions, this being due to the covenant being concluded with them at this time. I explained in connection with the covenant of the pieces G’d concluded with Avraham in Genesis 15,17 that Avraham observed G’d as if passing between the pieces of the animals Avraham had cut up. [I could not find this exegesis of our author where it is supposed to be. Ed.] This report of “seeing” a manifestation of G’d resurfaces when the new covenant is made after the sin of the golden calf has been forgiven in Exodus 34,3 where only Moses is allowed to be present, i.e. to look at the mountain before he ascends. Having outlawed visual contact by others, G’d proceeds to announce that He will make a new covenant (Exodus 34,10) replacing the one the Israelites had breached at the golden calf episode.