LOL Actually Protestants accept the words of God through scripture.
John 3:15 That whosoever believeth in him should not perish, but have eternal life. 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.
"Most assuredly, I say to you, he who hears My word and believes in Him who sent Me has everlasting life, and shall not come into judgment, but has passed from death into life." (John 5:24)
You see, it’s not “self declare” it’s simply accepting the words of God in scripture. That’s something Catholics don’t seem to do much of.
When Protestants tell me that they are saved and know that they are saved no matter what else they do for the rest of their lives, that is self declaration.