Calvin in the 1520's advanced the time clause that we're saved "at the moment" we first believe and he originated the idea of "receiving Christ as savior", which in 1950 became "Accepting Christ as personal savior".
Institutes of the Christian Religion (John Calvin)
Pg. 487 "Their meaning is NOT, that by faith in Christ an opportunity is given us of procuring justifications OR acquiring salvation, but that BOTH are given us. Hence, so soon as you are ingrafted into Christ by faith, you are made a son of God, an heir of heaven, a
partaker of righteousness, a possessor of life, and (the better to manifest the false tenets of these
men) you have not obtained an OPPORTUNITY of meriting, but ALL the merits of Christ, since they are communicated to you."
Page 408 "Surely he who thus speaks shows, that as soon as any one repents he will be ready to receive him, and that the rigor which he exercises in chastising faults is wrung from him by our perverseness, since we should prevent him by a voluntary correction."
Page 154 "Hence, Bernard truly says, that, in the present day, a door of salvation is opened to us when we receive the gospel with our ears, just as by the same entrance, when thrown open to Satan, death was admitted."
3. What keeps false doctrines going?
Protestants go by "The gospel is simple, salvation is simple, truth is simple" - Simplicity is intoxicating. The less one has to do to be saved, the more attractive God is. Everything revolves around that. The problem is: They go with a simple but unscriptural Gospel. When teachings sacrifice truth for simplicity, people prefer simplicity.
To support this gospel, what has developed is:
B. Protestants, live by
"A doctrine does not have to be directly stated in the Bible as long as the concept is there."
With this premise, anybody could claim any concept in the Bible. This loose approach gives protestant leaders a lot of wiggle room in their doctrines. Exs. of round about doctrine - First act of obedience is justified by Matthew 3:15 and 1 John 2:6, in the abscence of a scripture saying "Baptism is a christian's first act of obedience." Protestant leaders also use Revelation 3:20 and 1 John 1:9 as salvation scriptures even though they are not telling the Christians to whom they're addressed how to be saved.
C. They use modern day expression and philosophical reasoning to analyze first century Biblical scripture. For example John 1:12 did not in any way refer to those receiving Jesus 'as Savior', but to those who accepted that Jesus's claims were true. Protestants capitalize on the word receive out of context to support the sinner's prayer. In John 12:49-50 Jesus delivered God's words just as God wanted them - they are good enough.
D. Protestants do not encourage their members to study out for themselves the scriptures on salvation, especially before "being saved."
G. Protestantism and psychology.
-The altar call and the brain.
-Book: Made to Stick. (How humans come to accept ideas and doctrines.)
Simple, unexpected, concrete, credible, emotional, & stories.
(E.g.- Several false myths people still believe in - We use only 10% of our brains, Mary Magdelene committed sexual sin, & shaving makes hair grow back thicker.) The same 6 psychological processes that promote myths make people believe in false Biblical teachings.
In essence, although not always intentional, large institutions package things in an easy to understand way, complete with catch phrases, lingo, and slogans so that everyone within a given culture can follow along. It creates a momentum like the phrase 'Go green'. It's very difficult for people to doubt the validity of a teaching once a momentum has started - Accept Jesus as your personal savior, oh how beautiful.
I was very surprised to find out that Sherlock Holmes never said "Elementary, my dear Watson."