The Trinitarian nature of God (i.e., God existing in three equally Divine Persons, and yet being one God) just one of the incomprehensible teachings in Biblical orthodoxy - meaning, no human mind (which is just finite and therefore limited) can fully comprehend this teaching. As it is written in Deuteronomy 29:29 (quoting from MEV), "The secret things belong to the Lord our God, but those things which are revealed belong to us and to our children forever, so that we may keep all the words of this law."
For sure we can use some illustrations to which the Trinity can be likened. One of the illustrations is the water. In its normal state, the water is liquid, in it's solidified state an ice, and it its gaseous state a vapor. These are not three different waters, but only one water in three different states. This illustrates how the Three Persons are distinct from each other and yet being of one "substance" (Divine). The only problem is that this can confuse us into believing the Sabellian heresy. This heresy states that Jesus is the Father during the OT times, the Son after being born in Bethlehem, and the Holy Spirit during the church age. But this is not what the Bible teaches
Another illustration is the sun. In this illustration, the Trinity is likened to the sun, its light, and it's heat. As long as the sun exists, its light and its heat will continually exist. This illustrates how the Son and the Holy Spirit are eternally co-existent with the Father, that as long as the Father exists, the Son and the Holy Spirit will also exist. The only problem with this illustration is that this can confuse us into thinking that the Persons of the Trinity are just parts of one Godhead. But this is not what the Bible teaches.
We can read in the Bible two incidents where God the Father spoke from heaven about His Son (Matthew 3:16-17, 17:1-9), which clearly shows that Jesus is not God the Father, but rather the Son of God Who is already co-existing with the Father eternally before the creation of the cosmos (John 1:1-2). We can also read a passage in the Bible where Jesus called the Holy Spirit "another Comforter" (John 14:16-17, 26), which shows that the Holy Spirit is not Jesus, but rather another Person Who is also called "the Lord" (2 Corinthians 3:17).
So this is what the Bible teaches: There is only one God (Deuteronomy 6:4, Mark 12:29), Who exists in three distinct Persons - the Father, the Son, and the Holy Spirit. The Father is God (1 Corinthians 8:6, Ephesians 4:6), the Son Jesus Christ is God (John 1:1, Hebrews 1:6-8), and the Holy Spirit is God (2 Corinthians 3:17). Yet, there is not a triad of Gods, but rather only one God. How can this be possible? Again, we don't know. Remember: The secret things belong to the Lord our God (Deauteronomy 29:29).
- Shim'onai :D