There are people who will declare “all roads lead to God.” That is nonsense, and is so broad that it has no meaning whatever. If you claim to believe in everything, you actually believe in nothing. There are also priests who do not believe in God at all, which should be a reason to get out of the religion business, but it’s a paycheck, I guess.
One would imagine Pope Francis to be a little more solid in his Catholic beliefs, but he seems to be a little wobbly on the basic principles of Catholicism, which are that it is God’s church, and he is the Vicar of Christ, meaning Christ’s representative on earth. Catholic belief is that the church authority is granted through a line of priesthood starting with Peter, clear through the papacy to Francis, so in essence, all other churches are apostate. Maybe Francis didn’t get the message.
You also have those who “protested” against the authority of the papacy, as “Protestant” churches did centuries ago. Those traditional Protestant churches still hold that salvation comes only through Jesus Christ, and so there is a commonality of belief between Catholics and Protestants that recognizes Jesus as savior. That would seem to be a pretty good reason to develop unity and common cause between Catholics and Protestants, especially when Christianity in general is under attack and Christians are being murdered in the Middle East by Islamic warriors.
Other belief systems reject Christ entirely, including Islam, which believes Christ was a prophet but not the Messiah, and believes that salvation is through Islam and worship of Allah. The origin of Allah is murky, but he was probably a figure recognized as a moon god by the Sumerians and worshiped by Babylonians, Assyrians, and Akkadians, then worshipped by Arabs among a pantheon of about 360 gods until Mohammed elevated Allah above all the other gods, and then to the one and only God.
The weird thing now is that Pope Francis seems to be making nice with Islam, which is not necessarily a bad thing, though that issue of Muslims murdering Christians and driving them out from Muslim dominant nations in the Middle East should be a little troubling. But Francis is going well beyond trying to settle old rivalries, and that should be cause for alarm for anyone who professes a Christian belief.
See video and Pope Francis uniting with Islam on page 2: