The book is a βιβλαρίδιον [biblaridion] , little book, rather than a βιβλίον [biblion] , book.1 This book is differentiated from the scroll held by the Lamb (Rev. Rev. 5:8+). See Divine Similarities. The book is similar to the scroll (or book) which Ezekiel was instructed to eat (Eze. Eze. 3:1-2). Both Ezekiel and John are told to eat the book, both books were sweet to the taste but bitter in the stomach, and both books contained prophecy which the prophet was to ingest and deliver to other men (Rev. Rev. 10:9-11+ cf. Eze. Eze. 2:9-Eze. 3:4). This book is little because it contains a relatively lesser portion of the overall prophetic content within the seven-sealed scroll loosed by the Lamb (Rev. Rev. 5:1-2+). The contents of this little book are consumable and digestible by John whereas it is almost certain that he could never have ingested the full contents of the seven-sealed scroll. See commentary on Revelation 5:1 and Revelation 10:11.
open in his hand
Like the Lamb before the throne (Rev. Rev. 5:7-8+), this angel has a book in his hand. The Lambs book is said to be in His right hand but this angel appears to hold his book in his left hand because while holding the book he raises his right hand (Rev. Rev. 10:1+, MT and NU texts) in an oath. Whereas the Lambs book was originally sealed, this book is open. Open is ἠνεῳγμένον [ēneōgmenon] , perfect tense passive participle, having previously been opened . By now the Lambs book has had all seven seals removed (Rev. Rev. 8:1+) and probably lies completely open too. As intriguing as these similarities may be, this book is undoubtedly not the seven-sealed scroll for it is said to be smaller. Moreover, unless this angel is Christ, he is among those who are unworthy to even look at it (Rev. Rev. 5:3+), much less take hold of it (Rev. Rev. 10:8+).
his right foot on the sea and his left foot on the land
That which he places his feet upon he demonstrates his authority over (Deu. Deu. 11:24). The setting or planting of his feet on sea and land is the formal taking possession of both; or the formal expression of the purpose to do so.2 And is δὲ [de] which often indicates an adversative relationship: but. Left is εὐώνυμον [euōnymon] : Used by the Greeks as a euphemism for left, the left hand, the left side, as a replacement for ἀριστερός [aristeros] (left ) in opposition to the right, since omens on the left were regarded as unfortunate (Mtt. Mat. 20:21).3 His right foot (the side of favor) is placed upon the sea but his left foot (the side of disfavor) is placed on the land. This is a literal depiction with a possibly additional secondary symbolism: (1) the sea and land depict the entire physical globe; and 2) the sea represents the Gentile nations (Rev. Rev. 13:1+; Rev. 17:15+) while the land may represent the Jewish nation as stewards of the Promised Land (Gen. Gen. 13:15; Lev. Lev. 25:10-28; Lev. 27:24; 2Chr. 2Chr. 10:7; Ps. Ps. 83:12; Joel Joel 1:6; Joel 3:2).4 The authority the angel represents is complete: both geopolitically and nationally (Ps. Ps. 2:8; Ps. 89:25; Zec. Zec. 9:10; Mtt. Mat. 28:18; Eph. Eph. 1:22). The placement of the disfavored foot upon the land, if the land is representative of Israel, may indicate that judgment will begin with the Jewish nationthose who have the greater revelation and responsibility (Rom. Rom. 2:9 cf. Mtt. Mat. 10:15; Luke Luke 12:47-48). See commentary on Revelation 13:1 and Revelation 13:11. See Divine Similarities.
4 Since God was the ultimate owner of the land of Israel, since He had given tenant possession of the land to the people of Israel forever (Gen. Gen. 13:15; 2Chr. 2Chr. 10:7), and since the Israelites were only the tenant administrators of Gods land, they were forbidden to sell the land forever [Lev. Lev. 25:23]. . . If . . . an Israelite became so poverty-stricken that he was forced to sell the portion of land that was his tenant possession, he did not sell the ownership of the land. Instead, he sold the tenant possession or administration of the portion of the land for a temporary period of time (Lev. Lev. 25:16, Lev. 25:25-27). . . . God required that a sold tenant possession be returned to the original tenant or his heir in the year of jubilee (Lev. Lev. 25:10, Lev. 25:13, Lev. 25:28; Lev. 27:24).Renald E. Showers, Maranatha, Our Lord Come (Bellmawr, NJ: The Friends of Israel Gospel Ministry, 1995), 78-79.