The careful wording of the Trinity is meant to guard against polytheism and/or tritheism. In addition, it is guarding against Arianism which tries to remove Jesus from his position of coeternal with the Father, to the firstborn of creation. The WCF's statement on the Trinity matters today, as Muslims and many others make false claims about Christians worshipping multiple gods. To this assertion, the Second Helvetic Confession is very strong in its wording found in chapter three, section two: "We detest the multitude of gods because it is expressly written..." and then it provides the Shema and other various Scripture references referring to God as one. (Beeke 6) It further clarifies the issue in chapter three section three stating that "so that there are not three Gods, but three persons, consubstantial, coeternal, and coequal. (Beeke 20). Thus, it is not surprising to see a strong condemnation of Muslims in section 5 of chapter 3 when it states "We therefore condemn the Jews and the Mohammedans, and all those who blaspheme that sacared and adorable Trinity." (Beeke 20)
and against Jehovah's Witness which shares Arian views of Jesus. The Second Helvetic Confession expressly condemns relating to Jesus as one who is created in chapter 3 section 5.
In addition, Vos points out that unitarians flat out reject the Trinity, which is why it is so important that Reformed Christians, as well as all Christians, hold fast to confessing this foundational truth. (Vos 26)
Concerning the doctrine of the Trinity, Vos wisely articulates that Christianity stands of falls on this doctrine because the Bible represents the plan of salvation as a covenant among the persons of the Trinity. (Vos 27)