Does the success of the Iglesia Ni Cristo prove that it is of God?
The organization known as the "Iglesia Ni Cristo" often points to their success and global expansion as the proof that their movement is of God. Is this a sound conclusion? When we look at the facts, and at the Bible, we see that it is not.
Roman Catholicism has lasted longer, and that does not make it true.
If the fact that the INC has lasted for 100 years make it true, then that would also make Roman Catholicism true since it has lasted for nearly 500 years. However, both Protestants and INC members agree that Roman Catholicism is not true, so longevity does not prove truth.
Mormonism has grown larger, and that does not make it true.
If the fact that the INC has spread so far and grown so large makes it true, then that would also make Mormonism true since it has grown far larger than the INC. However, both Protestants and INC members agree that Mormonism is not true, so growth does not prove truth.
The INC position makes the first century church a false church.
In a message given to the ecclesiastical district of northeastern seaboard, Eduardo V. Manalo stated:
What does the Bible tell us? What does it mean if an undertaking, a religion is in decline or experiencing failure? This means it is not of God. Because that which is of God - its success cannot be hindered; such work will never fail.
Notice first, that although Eduardo V. Manalo claimed that the Bible says this, he does not have any verse that says such a thing.
Additionally, the INC also believes that the first century church declined until it ceased to exist for nearly 2,000 years. To hold this position consistently, the INC would have to say that the first century church, established by Christ, was not of God because they were in decline!
Of course, the first century church was the true church, and the INC is simply being inconsistent when they claim that the first century church was in decline and claim that decline is evidence of falsehood.
The INC has no legitimate reason to believe that its success is evidence of its truth. When they say this, they unwittingly call many false religions such as Roman Catholicism and Mormonism "true". When they say this along with their other doctrine they unwittingly call the first century church and their own, false. The INC cannot hold the position that the first century church was true and failed to have the success that Eduardo V. Manalo preached always accompanies the true church.
Instead of looking to success and global expansion as the mark of truth, we should instead look to the teachings and their conformity to what the Bible teaches. This is how we determine if a church is a true church.
Acts 17:10-11 (ESV) - 10 The brothers immediately sent Paul and Silas away by night to Berea, and when they arrived they went into the Jewish synagogue. 11 Now these Jews were more noble than those in Thessalonica; they received the word with all eagerness, examining the Scriptures daily to see if these things were so.
 Measuring from the Council of Trent.