This is a highly debated issue. Some..., well the Christians at least..., will say that God speaks in the plural, due to the fact He is a plural of persons - Father, Son, and Holy Spirit.
Some, such as contemporary Jews, say that God is speaking using the plural of majesty. However there is no Biblical precedent for this plural of majesty, neither in the Bible, nor the Hebrew language of that time - but i guess the argument can be used that maybe the Bible was employing it for the first time - to explain the fact there's no corroborating evidence for its usage.
As Trinitarian Christians, we will maintain, putting all the pieces of the puzzle together, knowing that God is a plurality of persons, that this is God speaking in a manner which reflects His multiple personhood.
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Some, such as contemporary Jews, say that God is speaking using the plural of majesty. However there is no Biblical precedent for this plural of majesty, neither in the Bible, nor the Hebrew language of that time - but i guess the argument can be used that maybe the Bible was employing it for the first time - to explain the fact there's no corroborating evidence for its usage.
As Trinitarian Christians, we will maintain, putting all the pieces of the puzzle together, knowing that God is a plurality of persons, that this is God speaking in a manner which reflects His multiple personhood.