From a pure observational standpoint, anyone can tell the nature of the Muslim god is NOT the same as the Christian/Jewish God.
From a biblical standpoint, Paul tells us that if an angel or another man gives another gospel, DO NOT BELIEVE IT. Well, an angel (supposedly Gabriel) told Mohammed a different gospel--do NOT believe it.
Historically, the message received by Mohammed instructed him to destroy ALL the temples in Mecca except for the temple of Allah (the moon god). Note that there was a different temple for EACH day of the year. Mohammed destroyed all of them except Allah's.
The fact that the Catholic Church "embraces" Muslims, IMHO, points to the statement by Pope Paul VI (?) that "the enemy has entered the sanctuary." Look what has happened to the church since the 1960s, especially considering the political/social leanings of the current pope.
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