1John 5:8 And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one.

Here's The Short Version:
    The endings of these verses are saying two completely different things, and that is the reason that the KJV translators made their translations in two different ways. The first ending in verse 7 says of the subjects, "these three are one", while the second ending in verse 8 reads "these three agree in one". The reason? Such precise translation reveals the oneness of our God.

    Starting with the latter verse 8, the reason the verse must be phrased "agree in one" is because the subjects of the sentence are three different things. No logical person would attempt to suggest that Spirit and water are the same thing. Likewise, no rational person would suggest that water and blood are the same substance. Verse 8 is speaking of three separate entities and therefore must read that they "agree in one" because they are in fact separate.

    But not so in verse 7. There-- the subjects presented are in fact the same Person. We know this from Isaiah 9:6, John 1:1, and that fact that since it was the Holy Ghost who overshadowed Mary, He must be the Father, present under that title. For this reason, the ending of verse 7 is translated "these three are one". I once heard a person advise to take note that verse 7 does not read, these three "make up" one, indicating separate entities. So then it is the difference between the two verses that points to the attribute of God being one.

    I'm sure that it is NO accident that they are presented together in God's word as they are.

God bless you with joy- today and always,
Michael