Verse 30: Then Joshua built an altar unto the LORD God of Israel (Deut. 27:4, 5) in mount Ebal…
[Then he built an altar, אָ֣ז יִבְנֶ֤ה] They he raised (Drusius, Masius). It is a verb of the future/imperfect tense; but אָז/then, as elsewhere, changes the future/imperfect into the perfect (Drusius, Masius). Thus אָ֚ז יָשִׁ֣יר, then Israel sang; אָ֣ז יַבְדִּ֤יל, then Moses severed (Kimchi in Drusius). Then, that is, with the city conquered (Vatablus). Indeed, this entire ceremony was prescribed in Deuteronomy 11 and 27, and was to be used by them as soon as they had crossed over Jordan: not without good reason, since it pertains to the solemn covenant, which it was right to enter into with God before the beginning of the war. Response 1: Therefore, the Talmudists maintain that all these things were done on the same day in which the Jordan was crossed. But that is hardly able to be true, nor were all those things able to be transacted within that space (Masius). Response 2: This perhaps may appear more likely soon after the Circumcision and Passover were accomplished (now, τὸ ὕστερον πρότερον, hysteron proteron, is common in the Sacred history), for favorable auspices for the great war to be conducted. Objection: But it appears to be a greater distance from Gilgal to Ebal and Gerizim (which were near Shechem, as it is said, and were about sixty miles from Gilgal according to the Talmudists), than the multitude of Israelites, with their enemies not yet subdued, could safely accomplish. Responses: 1. Gerardus Mercator maintains that Gerizim and Ebal were not far from Ai. But in this he is mistaken. 2. At that time their enemies were demoralized with great panic. 3. The danger was not less, while the entire vigor of the soldiers was circumcised. 4. Until the Israelites conducted themselves in a hostile manner, we did not see anyone that opposed himself as an enemy to them. 5. Even if that journey was a bit longer, nevertheless it was able to be completed through a continuous,unobstructed valley. Response 3: If these things were conducted after the overthrow of Ai, an answer is able to be given to the commandment of Moses, that what was predetermined was not so much the first day after the crossing (for thus it was necessary for the uncircumcised to give attention to these sacred rites), as the first suitable occasion that they were going to meet (Masius). Concerning this entire ceremony, see what things are on Deuteronomy 11:29; 27 (Bonfrerius).
Then, to wit, after the taking of Ai. For they were obliged to do this when they were brought over Jordan into the land of Canaan, Deuteronomy 11:29; 27:2, 3, which is not to be understood strictly, as if it were to be done the same moment or day; for it is manifest they were first to be circumcised, and to eat the passover, which they did, and which was the work of some days; but as soon as they had opportunity to do it, which was now when these two great frontier cities were taken and destroyed, and thereby the coast cleared, and the bordering people under great consternation and confusion, that all the Israelites might securely march thither. And indeed this work was fit to be done as soon as might be, that thereby they might renew their covenant with, and profess their subjection to, that God by whose help alone they could expect success in their great and difficult enterprise.
[An altar…on mount Ebal] Thus Deuteronomy 27:4, 5. Not likewise on mount Gerizim: because there ought only to be one altar (Serarius). The altar was for the use of sacrifice at that time, but for the sake of a monument unto posterity, as in Joshua 22 (Grotius).
Built an altar, to wit, for the offering of sacrifices, as appears from the following verse, and from Deuteronomy 27:5-7. In Mount Ebal. Why not on Mount Gerizim also? Answer. Because God’s altar was to be but in one place, Deuteronomy 12:13, 14, and this place was appointed to be Mount Ebal, Deuteronomy 27:4, 5, which also seems most proper for it, that in that place whence the curses of the law were denounced against sinners, there might also be the tokens and means of grace, and peace and reconciliation with God, for the removing of the curses, and the procuring of God’s blessing unto sinners.
 Hebrew: אָ֣ז יִבְנֶ֤ה יְהוֹשֻׁ֙עַ֙ מִזְבֵּ֔חַ לַֽיהוָ֖ה אֱלֹהֵ֣י יִשְׂרָאֵ֑ל בְּהַ֖ר עֵיבָֽל׃
 Numbers 21:17.
 Deuteronomy 4:41.
 Hysteron proteron is a rhetorical device which presents ideas in an order other than their logical or chronological.
 The distance is only about twenty-five miles in a straight line, but given the mountainous terrain, perhaps the journey was actually this long.
 Gerardus Mercator (1512-1594) was a renowned geographer and cartographer of Flanders. His work included a detailed map of the Holy Land, Amplissima Terræ Sanctæ Descriptio ad Utriusque Testamenti Intelligentiam (1537). Mercator’s interests included theology: He was a Roman Catholic, but had some Lutheran sympathies.
 Ai is roughly twenty-two miles from Shechem.
 See, for example, Exodus 23:27; Deuteronomy 11:25; Joshua 2:9.