Hello Omah, to put it simply the ''easy believism'' that you quoted is usually used as a term of mocking.
I'll tell you where it come from,The people who believe in works-salvation ridicule the Biblical idea of eternal security calling it easy believism or OSAS or once saved always saved.
As a person who believes in eternal security or easy believism I'll embrace the title,because the scriptures support it and all through time Christs followers have been mocked by outsiders. Christs people were first called Christians as a term of insult but it stuck because it makes sense to the true believers to be a slave to Christ,let the mockers keep mocking.
Here is my own idea of eternal security:
I don't believe I can lose my salvation and it's because salvation has been described as the eternal gift of God:
John 3:16
16 For God so loved the world, that he gave his only begotten Son, that whosoever
believeth in him should not perish, but have
everlasting life.
Ephesians 2:8-9
8 For by grace are ye saved through faith; and that not of yourselves: it is
the gift of God
Romans 6:23
23 For the wages of sin is death; but
the gift of God is eternal life through Jesus Christ our Lord
If God takes back the gift he told me I can keep forever,he is a liar.
If I have to work for it,it is not a free gift.
I cannot give back the gift because Gods will is greater than mine.
Therefore I believe salvation is a free gift for those who believe on Christ and cannot lose their salvation.