In England between 1980 and 2015 (35 years) Anglican church attendance halved, while Catholic and Methodist church attendance declined by two-thirds.(www.brin.ac.uk/figures/church-attendance-in-britain-1980-2015)
There is a similar story, albeit not yet so dramatic, in the USA.
There are masses of articles on the internet about the ongoing decline in church attendance within all the major denominations in the UK and the USA. All kinds of causes are attributed, but none of the articles I read suggests that the decline in attendance is due to the increasing secularization of the church, its departure from Biblical truth, its failure to preach the full gospel and its failure to fully involve members in evangelism. The church in general is hiding its light (the gospel) under a bushel. It has become salt that has lost its savour, fit for nothing except to be trodden underfoot.
For any product to sell well it must do what it says on the label and be marketed effectively. The label on the gospel says that those who by faith commit their lives to Jesus Christ and to doing what he says will have everlasting life in a new and perfect world to come, whereas those who reject him and his teachings will suffer painful and final destruction. That is what the Bible teaches. If church leaders do not believe what the Bible teaches, why should anyone else believe it? All that is left for the church to offer people is some kind of social club with religious overtones.
One survey discovered that in business around 20% of the staff are typically involved in sales, except in smaller companies where the proportion is higher - up to 40%. Within the membership of a church it is not unreasonable to think that 20% of the members could be gifted in evangelism if they were motivated and trained to engage in it. One in five of the church-building roles Paul lists in Ephesians are evangelists. Are church leaders in the UK and the USA spending 20% of their time training at least 20% of their 'staff' to be salesmen and women? Even that should be a bare minimum. I once spoke to the pastor of the Jotabeche Pentecostal Church in Santiago, Chile. At that time his church had a membership of 120,000 people. I asked him how it had grown so big. He said, "Every member is an evangelist."
Yet even the most talented salesmen will fail if they don't believe in the product they are selling. If the church leadership doesn't believe the gospel, how will their members believe it? And if their members are not passionately convinced that the gospel is the best and most urgent news that anyone can be told, what motivation do they have to share it?