Rashi comments (Devorim 1:13):
And understanding: -- who understand one thing from another. This is what Arius asked of Rabbi Yose: What is the difference between wise men and understanding men? A wise man resembles a wealthy money-changer: When people bring him "dinars" to examine [and exchange] he examines them, but when they do not bring them to him he (merely) sits and does nothing. An understanding man resembles a merchant money-changer, when people bring him money to examine, he examines them and when they do not bring it to him, he seeks about and brings money of his own.
The Lubavitcher Rebbe suggests that what is going on under the surface is a discussion of... Trinity:
"Arius was an early christian bishop who established a new denomination in christianity which emphasized unity in G-d, as opposed to the standard christian belief in the trinity. As a result of his "heresy," he was denounced, disrobed and exiled, but was later reappointed to his station.
The difference between unity and trinity in Arius's philosophy may be analogous to the difference between secular wisdom and understanding. Unity symbolizes the unitary spark of wisdom, while trinity alludes to the three stages of understanding. Therefore, Arius who represented unity (wisdom) questioned and challenged the "understanding" of trinity. "
The explanation is daring and striking. The curious application of Chabad categories of thought to christian sectarianism shows the incredible breadth of knowledge and universal scope of the Rebbe's concerns.
St. Nicholas beating up Arius (actually he looks like he is pulling his ear...):
Arianism was one of several heresies the fight against which submerged the Roman Empire in blood and undoubtedly hastened its demise. More, here.
This knowledge is of potential halachic significance in establishing various denomination as idolatrous, or not. Unitarians (or Oneness Pentecostalists) might not be halachically ovdei avodah zara (even according to those who would consider Christianity (shituf) avodah Zara) and it may be persmissible to enter their churches for a purpose.