[Exo 20:1-3 NIV] 1 And God spoke all these words: 2 "I am the LORD your God, who brought you out of Egypt, out of the land of slavery. 3 "You shall have no other gods before me...."
This is the NIV which is considered a premier English translation, so it is about as good a translation as we get. Therefore it has problems, but its as good a translation as can be obtained generally, and it treats the scripture in question the same way as most others. Soapy feels confident about it.
Soapy claims that God says to Israel the he is the one God or is one God, but it appears to be Moses who speaks to Israel on behalf of the LORD. There is no direct address to Israel as Soapy seems to claim. This lowers the authority of the speech from "God said to Israel" to something else. It is at best Moses saying it to Israel, not 'God' talking directly to Israel.
That is only half of what is wrong. In Moses words here in Exodus 20 is the phrase 'Your god', showing possession and creating a problem with Soapy using the modern term 'God' in the verse. The Hebrew term 'Eloheem' has been changed to 'God'. Why? 'God' is a philosophically derived English term implying a divinity that is over all people everywhere, but this scripture verse has the term 'Your' in it addressed to Israel. It is specific to Israel and not to everyone, not over everyone, not for everyone. It does not say "I am God" but "I am the LORD
your God" and is addressed not to everyone everywhere but to Israel. Therefore Soapy's appeal to it being about 'God' is shaky in spite of the translation. He is, after all, questioning large bodies of churchmen and using scripture as his solid basis. Shouldn't the scripture he uses support his position without translational trickery -- without sliding things around and tapping things in with hammers? Shouldn't he rely upon something that doesn't exclude all people other than Israel when talking about the God of all people everywhere?
Should we view everyone everywhere as Israel? If not, then this 'Elohim' should not be translated 'God', but it is. Soapy is not at fault for that, however he does make the mistake of criticizing catholics for not being able to find support for their ideas about trinitarianism in scripture but then mistakenly appeals to this scripture to support his own claims. He has no more support for his claim than the catholics have to their trinitarian one.
There is no Jewish scripture in which God says to Israel "I am one person: God." It is at best some semantic slidery that doesn't reflect the original intent of the verses claimed by Soapy.