Verse 2: And the people came (Judg. 20:18, 26) to the house of God, and abode there till even before God, and lifted up their voices, and wept sore…
The people came to the house of God, etc.; partly to mourn for the common loss, and partly to ask counsel from God about the repairing of it.
[They began to weep] With vengeance satiated, compassion is remembered (Grotius).
Verse 3: And said, O LORD God of Israel, why is this come to pass in Israel, that there should be to day one tribe lacking in Israel?
[Why…has it happened that…one tribe should be removed?לְהִפָּקֵ֥ד הַיּ֛וֹם מִיִּשְׂרָאֵ֖ל שֵׁ֥בֶט אֶחָֽד׃] Verbatim: to pass from Israel one tribe? (Montanus); that it should be missed (Junius and Tremellius). Hebrew: that it should be visited; a Metonomy of effect (Piscator). That it should be lacking (Septuagint), as if it were wanting in census and reckoning (Nobilius). That it should perish (Syriac), it should be subtracted (Munster). That is to say, What have we done, etc? It is finished concerning this tribe, unless thou, O Lord, find an unexpected remedy for this evil (Osiander). The ask that God would set forth to Himself a reason to preserve the tribe (Malvenda out of Junius).
Why is this come to pass? Etc.: Why hast thou given them up to such wickedness, and us to such rage, that the whole tribe should be in a manner lost? Hence it appears that they did not swear to root them all out, as is further manifest from the different matter and words of this oath, verse 1, which only denied them their daughters in marriage; and that concerning the people of other tribes who joined not with them in this business, which was, that they should be put to death, verse 5. And their sparing of those six hundred men in the rock Rimmon, verses 13, 14, plainly shows that they were not obliged by any oath or vow to extirpate them.
Verse 4: And it came to pass on the morrow, that the people rose early, and (2 Sam. 24:25) built there an altar, and offered burnt offerings and peace offerings.
[Now, on the next day] That is, since they had already obtained the direction that they were seeking, as it is explained in what follows (Junius).
[They built an altar] Question: Whether this was rightly done? Response: It appears that it was not: 1. because the Altar of the Tabernacle was there; 2. because only the one Altar was permitted to the Israelites. Nevertheless, I think that this was rightly done (Bonfrerius, thus Lapide, Junius, Martyr, Tirinus, Menochius). They did not sin, because they erected this Altar in the Sanctuary. Now, in Deuteronomy 16:2, it was only forbidden to offer sacrifices on an Altar outside of the Sanctuary. Indeed, it was unlawful without a Divine dispensation to erect an Altar outside of the place of the Tabernacle; but it was sometimes lawful to be done in the Tabernacle (Bonfrerius). This new Altar was erected on account of necessity. For, since all the Tribes were congregated, and many individuals were desiring to offer sacrifices (with the war triumphantly concluded [Bonfrerius]), the one Altar of the Tabernacle would not be sufficient to receive them (Lapide, Bonfrerius). This case of necessity is reckoned as an exception from that common law of one Altar (Lapide); as it is evident from the deed of Solomon, 1 Kings 8:64 (Bonfrerius, Lapide, Malvenda, Junius, Martyr). The requirement of the Law, that there be only one Altar, was to be restricted to the republic wandering in the wilderness, when the Altar was to be carried here and there, as Moses shows, Exodus 20:24 (Malvenda out of Junius). Doubtlessly this Altar was constructed by a singular revelation made through the High Priest (Martyr).
Built there an altar; not for a monument of the victory, as some say, but for sacrifices, as the next words show. Question: What need was there of this, when the ordinary altar was there, to which also they seem to be restrained, Deuteronomy 16:2? Answer: They are not there restrained to one altar, but to one place of worship, as is expressed; and therefore there might be in that place more altars than one, when the multitude of sacrifices so required, which was the case 1 Kings 8:61; and probably at this time, when all the tribes being met, they had many sacrifices to offer, some in common for all, and some peculiar to every tribe. Nay, other altars might be, and ofttimes were, erected in other places, by Divine direction or dispensation; as Judges 6:21, 26; 1 Samuel 7:9, 17; 11:15; 16:2, 5.
 Hebrew: וַיָּבֹ֤א הָעָם֙ בֵּֽית־אֵ֔ל וַיֵּ֤שְׁבוּ שָׁם֙ עַד־הָעֶ֔רֶב לִפְנֵ֖י הָאֱלֹהִ֑ים וַיִּשְׂא֣וּ קוֹלָ֔ם וַיִּבְכּ֖וּ בְּכִ֥י גָדֽוֹל׃
 Hebrew: וַיֹּ֣אמְר֔וּ לָמָ֗ה יְהוָה֙ אֱלֹהֵ֣י יִשְׂרָאֵ֔ל הָ֥יְתָה זֹּ֖את בְּיִשְׂרָאֵ֑ל לְהִפָּקֵ֥ד הַיּ֛וֹם מִיִּשְׂרָאֵ֖ל שֵׁ֥בֶט אֶחָֽד׃
 Hebrew: וַֽיְהִי֙ מִֽמָּחֳרָ֔ת וַיַּשְׁכִּ֣ימוּ הָעָ֔ם וַיִּבְנוּ־שָׁ֖ם מִזְבֵּ֑חַ וַיַּעֲל֥וּ עֹל֖וֹת וּשְׁלָמִֽים׃