I'm not sure what "the light comes on in ones mind of the truth of the gospel" means.
I just believe the scripture that Paul wrote which says that we are sealed when we believe/trust the gospel of our salvation per Ephesians 1:13. That word for "believe/trust" is the same one used here:
Rom 4:3 (AKJV/PCE)
(4:3) For what saith the scripture? Abraham believed God, and it was counted unto him for righteousness.
It's more than just an acknowledgment of something; it is belief with trust... but it requires no other action to receive it. Paul continues that same passage with this:
Rom 4:4-5 (AKJV/PCE)
(4:4) Now to him that worketh is the reward not reckoned of grace, but of debt. (4:5) But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness.
Paul makes a clear distinction between the belief/trust and any "work" to receive it.