'Hear, O Israel: The LORD our God, the LORD is one' (Deuteronomy 6:4). The Hebrew word for 'one' used here is 'echad' which means 'one' in the collective sense. There are several examples in English, such as 'flock', 'herd', and 'family', which refer to groups of birds, cattle and persons, yet collectively are one. So God is echad - 'one' in the collective sense.
The first name for God in the Bible - in Genesis 1:1 - is Elohim, which is plural, thus, literally meaning 'Gods'.
So 'In the beginning God [Elohim, plural] created the heavens and the earth'. and then later in verse 26 it says; 'The God [Elohim] said, 'Let us make mankind in our image''.
In Genesis 2:24 it reads 'a man leaves his father and mother and is united to his wife, and they become one flesh'. Can two persons really be one person, one body, one flesh? They are two persons but are one through their unity in love.
And this is how it is with the Trinity. 3 persons are one in the love they have for one another.
In John 17:11. Jesus, in his prayer to His Father, asked 'that they [his disciples] be one as we are one'. Jesus is stating that He and God the Father are 'One' in the same way that Jesus' followers are 'one' in our love for one another.
- paraphrased from 'Three in One' from Sign of the Times, January 2020
'Two is better than one, but a cord of 3 strands is not easily broken' - Ecclesiastes 3:12
