This is what I believe the falling away is before the coming of the man of sin,the beast.
The Bible says that in the latter times some shall depart from the faith,giving heed to seducing spirits,and doctrines taught by devils.
These people did not depart from the Bible but departed from the truth of it,which I believe is they interpret the Bible that exalts people and is based on nature worship.
This will go on for some time which then this scripture applies that says,for the time will come when people will not endure sound doctrine,the truth,but according to their on lusts will they heap to themselves teachers,having itching ears,and will turn their ears from the truth and be turned unto fables.
The devil will use a false interpretation of the Bible to deceive the world,an interpretation that all religions will accept,which will prepare the way for the man of sin.
During the 7 years tribulation the first three and one half years they will operate by a one world government and a one world religious system.
The one world religious system will be all religions united and people can practice any religion they want but they cannot try to convert someone to their religion or they will be guilty of a hate crime punishable in the international court system.
They can practice any religion they want for all religions are valid as truth and everybody has their own path that leads to the same spiritual destination.
People can practice their own religion but the main theme of the one world religious system will be that false interpretation of the Bible which all religions will accept for Jesus is not the savior but a good teacher as well as other teachers.
Whoever is the spiritual leader of the one world religious system will be someone that believes the Bible but believes that false interpretation of the Bible and will impact all religions with that interpretation therefore impacting all nations.
The religious leader will prepare them for the coming of the man of sin who will be a man claiming to be God by tapping in to nature,who will not believe in a personal God but will honor the God of forces,or energy of the universe,which he believes is at his disposal to use,who will be in to witchcraft and a nature worshipper.
That false interpretation of the Bible based on the exaltation of man and nature worship that will impact the world during the one world religious system will cause people to stop believing in fundamental Christianity but they will believe it according to that false interpretation that exalts people,which that goes with the scripture the time will come they will not endure the truth but will want to hear the Bible according to their own lusts,which that false interpretation will give them as it exalts people.
These people will want to hear it according to their own lusts which means they want personal power and to exalt themself.This will go on for the three and one half years of the one world religious system.
The Bible says that the saints will not be united with Christ until there is a falling away first and the man of sin steps in to the Jews temple,which they will rebuild shortly,claiming to be God,and that is because as long as the world can repent of their sins the saints will not be united with Christ.
When the world takes the mark then they cannot repent of their sins anymore and the saints can be united with Christ.
So I believe the falling away is when during the one world religious system,the main theme of it will be that false interpretation of the Bible that will impact all religions and all nations until nobody wants to hear the truth of the Bible but want to hear that false interpretation,which takes away the hope of the world.
Since they do not want to accept the truth of the Bible but want to only hear that false interpretation that covers the world,it will prepare the way for the man of sin to be able to deceive them when he appears claiming to be God.
The devil will use that false interpretation of the Bible to deceive the world and to take away the hope of the world,an interpretation that fits the man of sin's agenda,which is to establish a world that does not believe in a personal God.
So to make it short,there has to be false interpretation of the Bible to deceive the world,to where they will only accept that interpretation,an interpretation that fits the man of sin's agenda,which will be based on the exaltation of people and being able to get power through nature.