One of the key things to correctly understand the way Jesus used the phrase is to see the reaction Jesus would get.
He was seen to be calling himself "equal with God"

and they wanted to kill him for that.

So its not just talking about being united as one in agreement.

Or in purpose

Or in organization.

That would not have gotten the reaction that Jesus got...for even the Old Testament prophets had stated as much.
No, rather when Jesus spoke this it was aimed at teaching us that there is no difference in his nature with the Father.

This was a rather shocking thing for Jews to hear...a man making the claim to be equal in nature with Almighty God!