What real Biblical proof is there for the trinity as we believe it? I do believe that t is necessary for us to believe that the Father, Son and Holy Spirit ARE all God but is it necessary for us to know HOW they are all God?
Evidence from scripture concerning the "triunity" of God?
God exists as one God. God exists as three persons, Father, Son and Holy Spirit. Modelism (which has been discussed in other threads) denies that God exists as three persons.
Let's take a look.
Lev. 6:4 "
Hear, O Isreal! The LORD is our God, the LORD is one!
Jesus repeats this truth in Mark 12:29.
Just from these two passages we establish that God exists as One God.
John 1:1 "
In the beginning was the Word, and the Word was with God and the Word was God."
This passage establishes a relationship within the Godhead between God (later identified as the Father) and the Word (later identified as the Son).
The Word (Son) has a three-fold equality with God the Father. He has a temporal equality (in the beginning....notice the language from Gen. 1). He has a positional equality (the Word was with God....face to face). He as an equality of essence (the Word was God....or deity...everything that makes God..."God"...the Word has as well.)
John 1:2 makes clear that a different "person" is being spoken of. "
He (literally...this One)
was in the beginning with God".
So, scripture has established that God exists as One God and as more than one person.
What about Holy Spirit?
John 14:26 "
But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your rememberance all that I said to you."
The passage makes clear that Holy Spirit exists as a separate person from God the Father and God the Son. "
the Father will send in My name, He will teach you..."
Acts 5:3 "
But Peter said to Ananias, why has Satan filled you heart to lie the Holy Spirit........(4)....
You have not lied to men, but to God."
This passage establishes that Holy Spirit is God.
So, these passages (and many others BTW) establish the truth that God exists as One God and that God exists as Three Persons.
Someone earlier spoke of the mystery of God. Since there is no one like God that exists, we have no one to compare Him to (all analogies fail at some point).
God condescends to us, revealing truth about Himself, how He exists. Everything He has taught us is true, but I don't believe we are able to comprehend any more than what He has revealed to us.
That being said, we ought to believe what God has revealed in His Word.
To answer your question about how much understanding of God existence is "necessary" (I assume you mean for salvation).... logically it doesn't appear from scripture that much understanding of the nature of the Godhead is necessary for salvation.(Acts 16:31)
However, salvation is accompanied by indwelling Holy Spirit. I believe Holy Spirit convicts all Christians of the truth of God's Word and the plain meaning of it.
If, then, someone is denying God's Word on an issue that is as clear and as important as the nature of the Godhead (One God, Three Persons) it could be they are Christians in need of more instruction or it could mean (after repeatedly rejecting the truth of God's Word) that they aren't really Christians.
In the final analysis, we can't know for certain which one of these options apply to the person who denies the triunity, because we cannot see inside them and determine if Holy Spirit indwells.
We may, imho, say that such a person as would repeatedly deny the triune nature of the Godhead shouldn't have assurance of their salvation since they are denying a great truth that God has seen fit to reveal to us, His children, about Himself.
peace to you

raying: