Important clarifications, page-178

Believest thou notthat I am in the Father, and the Father in me? the words that I speak unto youI speak not of myself: but the Father that dwelleth in me, he doeth the works.

John 3:34 - For He whom God sent speaks the words of God; for (because Luke 4:18) He does not give the Spirit sparingly.

Your quote is Jesus's answer to showing them the Father and the only works referenced here, are the Father words coming out of Jesus, which Jesus deems as seeing (perceiving - Interlinear) the Father.

So when Jesus spoke the Fathers words, he became the express image of his person Heb 1:3 KJV.

I believe we have a twofold message there.
1. The Holy Spirit there which is the Fathers Spirit (Him), was dwelling in Jesus, aiding him to speak the words of the Father.
2. They are one in word, Jesus accepts the Father words, the messages that they bring and makes them his way of life, they in effect become him.
Likewise, the Father is of the same mind, this is also referred to as the spirit of them, hence the context of I am in the Father and the Father is in me.

Likewise, if you and I were on the same page, as per the above, we could rightfully say, we are in each other or come in the spirit of the other.
To quite a degree, we are our word, our words expressed are our spirit person or the us, expressed.

You have probably heard the saying, we become what we eat, likewise with the words/messages that we take in and adopt.
Another example or saying, you become who you associate with.