According to Their essence, the three are one; thus, there is the aspect of the essential Trinity. The Son is the embodiment of the Father (Col. 2:9), and the Spirit is the reality of the Son (John 14:16-18).
A Son is given to us, yet His name is called the eternal Father (Isa. 9:6).
The Son as the last Adam became the life-giving Spirit (1 Cor. 15:45b). He was incarnated to be the flesh. He was the last Adam. That means that after Him, there would be no flesh. He was the ending, the closing, the concluding, of the flesh. This One in resurrection became the life-giving Spirit. Thus, this One, the Son, is the Father and eventually He is the Spirit. In 1934 Brother Nee gave a conference on the all-inclusive Christ. He said that Christ, the all-inclusive One, is the centrality and universality of God. He is the Son, yet He is the Father. He is the Son, yet He is the life-giving Spirit. Thus, He is the centrality and universality of the Triune God.
The Lord is the Spirit (2 Cor. 3:17) and the Lord Spirit (v. 18). The Lord Spirit is a compound divine title like the Father God. He is both the Lord and the Spirit. They two are one in Him.
Such words in the Scripture are strong evidence that the Father, the Son, and the Spirit are essentially one.
When we speak of the Triune God according to His economy, we are speaking of Him according to His moving and acting, not His essence. According to the economy, the three are three; thus, there is the aspect of the economical Trinity. The Father is the Originator, making the divine economy (Eph. 1:9-10; 3:9; 1 Tim. 1:4b); then the Son accomplishes the divine economy made by the Father (John 5:19; 8:28); and the Spirit applies to God's elect what the Son has accomplished (16:13). These are steps of one complete move. God the Father planned to do something; the Son accomplished the plan; and the Spirit applies to us what the Son has accomplished. They are still one in harmony in the economical Trinity (10:30; 17:21, 23).