Christians did not invent the triune nature of God. The bible declares it. The word “trinity” is a word coined to express what God’s Word affirms. God’s Word simultaneously affirms that there is only one God, and that the Father is God, Jesus is God, and the Holy Spirit is God. Some try to escape this by suggesting that there are three Gods. Some even see a plurality of gods with humans having the potential to become gods. Some try to see God as performing three roles in succession. Each of these approaches will not stand the test of careful searching of the Scriptures. When Jesus could speak of the Heavenly Father as being one with Him, He did not merely mean that the Father was in unity with Him. When He spoke of the Holy Spirit and then said that He would come to us, He obviously meant that the Spirit was one with Him as well. There is no jealousy with God. Whatever the Father does, the Son does, and the Spirit does as well. These truths arise from divinely revealed Scripture. They may stretch us or challenge us, but there they stand. There is only one God, and He has revealed himself in three persons. The Father, Son, and Spirit, are equal and eternal.
Read the first chapter of John’s gospel and note that the “Word” of which John speaks is Jesus Christ. Read also John 14:15-18 and note that Jesus simultaneously speaks about going away and the Counselor who will come. In that same context He says, “… I will come to you”. When the Spirit comes to us, Jesus has come to us. That is why we can say Jesus lives in our heart. Notice also that the Counselor comes from the Father. Many many other texts reveal these truths.