Here is how to answer a Jehovah’s Witness or any other cults that deny the Trinity.
1) Jesus shares the name and titles of God the Father (Exodus 3:14; John 8:58). Jesus who came before Abraham, was the one who spoke to Moses at the burning bush. The claim to deity is a factor. Otherwise, why would the religious leaders who subscribe to monotheism try to kill Jesus?
2) Inconsistency and poor understanding of Greek grammar. The New World Translation from John 1:1 says, “In the beginning was the Word, and the Word was with God, and the Word was a god.” Why do they substitute “a god” for “was God?” Part in parcel is due to the absence of a definite article. However, an absence of a definite article does not grant one a license to translate into “a god.” Moreover it undermines the last verb tense which is in the “imperfect” (grammar demands “was God”). Moreover, to be consistent, NWT must translate passages that is absent of the definite article in reference to God the Father as “a god.” They won’t do it because it will undermine their aberrant theology. Their inconsistency reveals their self-defeater.
3) Misuse of Greek grammar in Colossians 1:15. “Firstborn comes from the Greek word πρωτότοκος (prōtotokos) which connotes the idea of preeminence and first in rank. Jehovah’s Witness disastrously confuse firstborn with first created. As a result, their faulty presupposition of Christ has allowed them to translate Col. 1:16 as “Because by means of him all other things were created…” Proper translation would be “For by Him…” Jesus was the major agent of creation. A god cannot share attributes of creatorship. Only God has the attribute of creatorship. Their teachings runs in contradiction to Isaiah 40-48. Moreover John 14:28 use of the word “greater” is not referring to the ontological nature of Christ. Functionally as the God-man, He operates in a subordinate role to the Father. But Him and the Father are one. (John 10:30). In other words, Jesus shares the honors, attributes, names, deeds, and seat of the Father. A god cannot share those qualities.
4) Jehovah’s Witness like many other false religions are self-righteous. In Luke 18:18-19 says, “And a ruler asked him, ‘Good Teacher, what must I do to inherit eternal life?’ 19 And Jesus said to him, ‘Why do you call me good? No one is good except God alone.'” A contrasting device is used here to reveal the young ruler’s self righteousness. The Jehovah’s Witness is liken to the young ruler. Moreover, the parable of the young ruler also refers to Jesus as good. John 10:11 says, “I am the good shepherd; the good shepherd lays down His life for the sheep.”
5) Point out their false prophecies. In 1972 the Jehovah’s Witness Watchtower claimed to be the prophet of God. These false prophecies are clear violations of Deuteronomy 18:22, “When a prophet speaks in the name of the Lord, if the thing does not come about or come true, that is the thing which the Lord has not spoken. The prophet has spoken it presumptuously; you shall not be afraid of him.”
CARM documents:
IDENTIFYING THE “PROPHET”–“So does Jehovah have a prophet to help them, to warn them of dangers and to declare things to come? These questions can be answered in the affirmative. Who is this prophet? . . . This “prophet” was not one man, but was a body of men and women. It was the small group of footstep followers of Jesus Christ, known at that time as International Bible Students. Today they are known as Jehovah’s Christian Witnesses . . . Of course, it is easy to say that this group acts as a ‘prophet’ of God. It is another thing to prove it,” (Watchtower, Apr. 1, 1972, p. 197). (See Deut. 18:21).
1897 “Our Lord, the appointed King, is now present, since October 1874,” (Studies in the Scriptures, vol. 4, p. 621).
1899 ” . . . the ‘battle of the great day of God Almighty’ (Revelation 16:14), which will end in A.D. 1914 with the complete overthrow of earth’s present rulership, is already commenced,” (The Time Is at Hand, 1908 edition, p. 101).
1916 “The Bible chronology herein presented shows that the six great 1000 year days beginning with Adam are ended, and that the great 7th Day, the 1000 years of Christ’s Reign, began in 1873,” (The Time Is at Hand, forward, p. ii).
1918 “Therefore we may confidently expect that 1925 will mark the return of Abraham, Isaac, Jacob and the faithful prophets of old, particularly those named by the Apostle in Hebrews 11, to the condition of human perfection,” (Millions Now Living Will Never Die, p. 89).
1922 “The date 1925 is even more distinctly indicated by the Scriptures than 1914,” (Watchtower, Sept. 1, 1922, p. 262).
1923 “Our thought is, that 1925 is definitely settled by the Scriptures. As to Noah, the Christian now has much more upon which to base his faith than Noah had upon which to base his faith in a coming deluge,” (Watchtower, Apr. 1, 1923, p. 106).
1925 “The year 1925 is here. With great expectation Christians have looked forward to this year. Many have confidently expected that all members of the body of Christ will be changed to heavenly glory during this year. This may be accomplished. It may not be. In his own due time God will accomplish his purposes concerning his people. Christians should not be so deeply concerned about what may transpire this year,” (Watchtower, Jan. 1, 1925, p. 3).
1925 “It is to be expected that Satan will try to inject into the minds of the consecrated, the thought that 1925 should see an end to the work,” (Watchtower, Sept., 1925, p. 262).
1926 “Some anticipated that the work would end in 1925, but the Lord did not state so. The difficulty was that the friends inflated their imaginations beyond reason; and that when their imaginations burst asunder, they were inclined to throw away everything,” (Watchtower, p. 232).
1931 “There was a measure of disappointment on the part of Jehovah’s faithful ones on earth concerning the years 1917, 1918, and 1925, which disappointment lasted for a time . . . and they also learned to quit fixing dates,” (Vindication, p. 338).
1941 “Receiving the gift, the marching children clasped it to them, not a toy or plaything for idle pleasure, but the Lord’s provided instrument for most effective work in the remaining months before Armageddon,” (Watchtower, Sept. 15, 1941, p. 288).
1968 “True, there have been those in times past who predicted an ‘end to the world’, even announcing a specific date. Yet nothing happened. The ‘end’ did not come. They were guilty of false prophesying. Why? What was missing? . . . Missing from such people were God’s truths and evidence that he was using and guiding them,” (Awake, Oct. 8, 1968).
1968 “Why are you looking forward to 1975?” (Watchtower, Aug. 15, 1968, p. 494)
6) Point out the implications of denying the biblical Christ. See John 3:36; Romans 5:8-9. Denying Christ undermines “relational intimacy” with God the Father which only Christ can provide. A false Jesus who is a god cannot bring you near a Holy and just God (John 14:6).
7) Old Testament passages like Psalm 102:25-27 points to the supremacy of Christ. Hebrews 1:10-13 affirms that truth. In fact tell the Jehovah’s Witness to turn to his or her NWT.