@Cheeky200386, The issue comes about because there is a difference between the two major Bible manuscript streams. One stream has the words "and he stood on the shore" as the end of Revelation 12:17. The other stream has the words "and I stood on the shore" as the beginning of Revelation 13:1.
Plus the former has the Greek word ἐστάθη and the latter has the Greek word ἐστάθην. You will notice there is only one letter difference between the two. But the first is the
third person singular (he/it stood) and the second is the
first person singular (I stood).
As a Greek scholar has said:
"The choice of which is proper here really stands or falls on your position on the three chief critical texts (Sinaiticus, Alexandrinus & Vaticanus), you either accept their pedigree or do not. The passage makes sense (though with slightly different implications) either way and no great doctrine hangs upon either reading. The context and the flow of the passage admit either without great preference. Therefore it is really a question of whether to accept the critical text sources or the majority text sources."
So, we either have:
"And the dragon was angry with the woman, and he went to make war with the rest of her children keeping the commandments of God and holding the testimony of Jesus. And he stood upon the sand of the sea. And I saw rising out of the sea a beast, having ten horns, and seven heads, and on its horns, ten diadems, and upon its heads, names of blasphemy."
Or we have:
"And the dragon was angry with the woman, and he went to make war with the rest of her children keeping the commandments of God and holding the testimony of Jesus. And I stood upon the sand of the sea. And I saw rising out of the sea a beast, having ten horns, and seven heads, and on its horns, ten diadems, and upon its heads, names of blasphemy."
Take your pick. I side with the scholar above who says "no great doctrine hangs upon either reading" because he is correct. You won't go wrong with either.
So why did God permit these variants in the transmission of His Word down through the ages? I think He permitted them in order to prove the authenticity of His Word.
First of all these variants (which seem to have been introduced through small copyist errors) do not affect any important doctrine. (I would suggest they do not affect any doctrine at all; at least i have never found one.) But their existence among the thousands of diverse manuscripts proves that no single entity could have altered the overall text, proving that the overall Word of God that we have is indeed the authentic Word of God. Do you see? The existence of small variants among literally thousands of ancient manuscripts proves the Bible's authenticity because if some entity had conspired to alter the Bible, there would be no variants: every manuscript would be identical. As someone has said, God preserved His message to us through the sheer volume of its transmission while at the same time proving that its message has not been altered. Glory to His name!
I hope this helps.