Isaiah 9:6-7 are famous verses of the Old Testament which clearly prophesied the ministry of the Messiah. However, the verses have created debate because some interpreted the word “Father” here as God the Father in the Godhead, affirming that God the Son (Christ) and God the Father are one and the same. This view contradicts traditional Trinitarianism. Superficially, this belief may seem reasonable, but actually it is not. The intent of this article is to refute this notion based on the context of the Book of Isaiah, the usage of the word “Father/father” in the Old and New Testaments as well as the doctrine of Trinitarianism as it is consistently affirmed through the revelation of the whole Bible. The writer believes the key point here is not scriptural translation, but rather interpretation. We must be careful when considering such an important element of our faith as the Trinity. We cannot use the Old Testament to judge the New Testament, but rather the New to interpret the Old. This is an important principle. Because it was not until the New Testament time the Lord declared the mystery personally and the Apostles preached it continually. The doctrine of the Trinity was hidden and obscure in the Old Testament time, and never clearly revealed. So we cannot clarify the Persons of the Trinity based on Old Testament scriptures and certainly cannot rely on one verse to finalize such an important doctrine. It is very dangerous and also contradicts proper exegesis with an obviously “private interpretation” (2 Peter 1:20). The wrong interpretation produces the wrong doctrine. The wrong doctrine builds up the wrong faith, leading eventually to wrong practices and distorted experiences. There will be shortages and errors on the path of the faith if believers deviate from knowledge of the truth of the Triune God. It is a serious thing. Through proper exegesis, “rightly dividing the word of truth” (2 Timothy 2:15), we can go back from a wrong interpretation to a right one. Because only by clarifying the source of our belief can we set up an accurate doctrine and bring the children of God back to the right faith.