Fausset's Bible Dictionary
TOBIAH or TOBIJAH ("goodness of Jehovah".)
1. A Levite employed by Jehoshaphat to teach the law in the cities of Judah (2 Chronicles 17:8).
2. "The slave, the Ammonite." With Sanballat and Geshem tried by fair means and foul to thwart Nehemiah (Nehemiah 2:10; Nehemiah 2:19; Nehemiah 6:17-18; Nehemiah 13:1-8). He had the greater power of mischief, being married into a Jewish family (the daughter of Shechaniah), and having his son Johanan married to the daughter of Meshullam, thus he had a Jewish party on his side. As Sanballat represented Moab's hereditary grudge against Israel, so Tobiah represented Ammon's. Eliashib was allied to Tobiah; possibly Sanballat, Eliashib's son in law, was related to Tobiah, and so Tobiah was connected with Eliashib (Nehemiah 13:4). Hence, it was deemed necessary to read before the people the law that "the Ammonite and the Moabite should not come into the congregation of God forever" (Nehemiah 13:1). Tobiah was notorious for contemptuous sarcasm (Nehemiah 4:3-5), "even that which they build, if a fox go up, he shall even break down their stone wall."
Nehemiah winced under his scorn and appealed to God for vindication: "hear, O God, for we are despised, and turn their reproach upon their own head." The psalmist of Psalm 123 (possibly Nehemiah) speaks in the person of Israel similarly of Moab's, Ammon's, and Samaria's contempt: "behold as the eyes of servants look unto the hand of their masters (glancing in contrast at 'Tobiah the servant' or slave) so our eyes wait upon the Lord our God ... Have mercy upon us, for we are exceedingly filled with contempt; our soul is exceedingly filled with the scorning of those that are at ease, and with the contempt of the proud." An undesigned coincidence between the psalm and the history.
So also Psalms 79:4; Psalms 79:12, written at the same date (see Psalms 79:1) when the "holy temple" lay "defiled": "we are become a reproach to our neighbours, a scorn and derision to them that are round about us ... Render unto our neighbours sevenfold into their bosom their reproach wherewith they have reproached Thee." Tobiah corresponded with the nobles of Judah of his party, many of whom were "sworn to him" because of affinity. These reported his good deeds before Nehemiah to win him over, and then reported Nehemiah's words to Tobiah, and wrote intimidating letters to Nehemiah (Nehemiah 6:17-19). His crowning impudence was residing in a chamber of the temple, of which the proper use was to be a store for the vessels, the tithes, and offerings for the Levites, priests, etc., Eliashib having dared, in defiance of the law, to prepare it for him. Nehemiah was sorely grieved, and cast all Tobiah's stuff out, and commanded the cleansing of the chambers (Nehemiah 13:1-9).
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Fausset, Andrew R. Entry for 'Tobiah'. Fausset's Bible Dictionary. https://www.studylight.org/dictionaries/eng/fbd/t/tobiah.html. 1949.