Many think that the Trinity is blasphemous. They think that it is a form of polytheism that violates the oneness of God. They think it is associating a partner with God. They think it is sinful speculation into the nature of God. It does not do any of these.
For the doctrine of the Trinity to be blasphemous it would need to fulfill at least one of these three conditions:
The doctrine of the Trinity does not try to make a man out to be God. So much of the doctrine is based on Jesus' own words concerning himself that he was more than a man; that he came from heaven, that he had a special relationship of Son to the Father from eternity, that he identified himself with the angel of the Lord of the Old Testament, and that he said and did things that are only proper for God Himself to say and do. Jesus made himself out to be more than a man. In the Trinity, Christians are only accepting and trying to accurately work out Jesus' words about himself and his relationship to God the Father and the Holy Spirit.
The Trinity does not say there is more than one God. It is an attempt to explain what the Bible reveals about the One God, that within this one, there are three persons sharing the one essence in perfect unity. Though this is hard to understand, it is not polytheism.
The Trinity also is not arrogant speculation about God's nature. It is an honest, reverent, attempt to express the fullness of what Holy Scripture reveals about God. It stays within the bounds of the revelation of the Bible. It is not an idea that is a human invention.
B. Why is it reverent?
C. Conclusions
"The secret things belong to the Lord our God, but the things revealed belong to us and our sons forever, that we may observe all the words of this law." (The Torah, Deuteronomy 29:29)