Fausset's Bible Dictionary
Used to stamp a document, giving it legal validity. Judah probably wore his suspended from the neck over the breast (Genesis 38:18; Song of Solomon 8:6; Job 38:14). As the plastic clay presents various figures impressed on it by the revolving cylinder seal (one to three inches long, of terra cotta or precious stone, such as is found in Assyria), as "it is turned," so the morning light rolling on over the earth, previously void of form through the darkness, brings out to view hills, valleys, etc. Treasures were sealed up (Deuteronomy 32:34); the lions' den in Daniel's case (Daniel 6:17); so our Lord's tomb (Matthew 27:66).
Sealing up was also to ensure secrecy (Daniel 12:4; Revelation 5:1). The signet ring was the symbol of royal authority (Genesis 12:41-42; Esther 3:10; Esther 8:10). Clay hardens in the heat, and was therefore used in Assyria and Babylon rather than wax, which melts. A stone cylinder in the Alnwick Museum bears the date of Osirtasin I, between 2,000 and 3,000 B.C. The Assyrian documents were often of baked clay, sealed while wet and burnt afterwards. Often the seal was a lump of clay impressed with a seal and tied the document. Such is the seal of Sabacho or So, king of Egypt (711 B.C.), found at Nimrud (2 Kings 17:4).
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Fausset, Andrew R. Entry for 'Seal'. Fausset's Bible Dictionary. https://www.studylight.org/dictionaries/eng/fbd/s/seal.html. 1949.