Do I need to say my salvation prayer out loud instead of praying silently?
Yes. Confession is verbal: Scripture says to confess with your mouth the Lord Jesus, and the teaching urges saying it out loud when calling on Him for salvation, rather than merely assuming God reads the heart, although He certainly can.
Les teaches that when a person calls on Him for salvation, they should verbalize it and say it out loud. He says not to just assume God reads the heart, although He certainly can, because God wants us to actually audibly say it: 'Lord, I want you to save me. I believe that what you've done, you've done on my behalf.' The context connects this to confessing with thy mouth verbally the Lord Jesus. It also stresses believing in the heart that God raised Him from the dead, implying Christ died and rose again, with the promise, 'Thou shalt be saved.'
More Questions
Do I have to say a prayer out loud to be saved, or can God just read my heart?
You should not merely assume God reads your heart (though He certainly can); He wants you to audibly say it out loud, calling on Him for salvation in words like 'Lord, I want you to save me. I believe that what you've done, you've done on my behalf.'