Trinitarians point to Zechariah 13:7 and claim God has an equal. There "the Lord of hosts" speaks of a shepherd as "the man, my associate." Trinitarians say "associate" means "equal." That means the shepherd associate is a person "equal with God."
Trinitarians also tell us the Lord of hosts is really THREE PERSONS. Those three Persons compose one entity or being. The three distinct Persons of the Trinity are one God, not three Gods.
However, you might at this point be prone to ask, "But doesn't that make four persons? Three are in heaven as the Lord of hosts, and one is on the earth as the shepherd associate."
A Trinitarian friend will respond, "Well, no, not exactly. You see, one Person of the Trinity is a God-man. He has both God's nature and man's nature."
But that leads to another question: "Does this mean half of one of those persons is in heaven and the other half is on earth? Doesn't that make two persons separated by the vast exspanse of universal space? And doesn't that mean they are actually two separate beings, one with a spirit body in heaven and the other with a physical body on the earth?
Perhaps feeling a bit confused by the question, our Trinitarian friend might say "Well, no. The shepherd on earth is the God-man. When Jesus was on the earth he was both God and man. Now in heaven he is still both God and man, having both the divine nature and human nature.
You may feel that this leads to still another question: "Does this mean, then, that in Zechariah's day, when the Lord of hosts spoke of his shepherd associate, that he was really only two persons of the Trinity? In other words, they were in heaven, and the God-man was on the earth. If the Trinity in heaven was composed of three persons, wouldn't that make four members of the Trinity if we include the person on earth?
Now, these are not the kinds of questions that Trinitarians want to hear. Such questions indicate you are probing too far into the deep things of God. Before you decide to ask any more questions, your Trinitarian friend and guide will probably suggest that we all move on to another topic.
If you do probe deeper, you may discover that Trinitarians actually worship three gods, after all. It is much better for the sake of your salvation to conclude that the Trinity is a mystery not to be understood by finite minds such as ours.
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