Well, since no one is brave enough to answer the question, I'll answer it:
What must I do to be saved?
Believe. Aorist. Punctiliar action. An event. Mental assent.
And I will be saved. Indicative. No ifs, ands, or buts. It will happen.
Know what happens when you stop believing? You've still believed in the aorist, and it cannot be undone.
It's like squeezing the trigger on a gun. Once that round has been fired, you can't unsqueeze the trigger and have the round come back.
Now, in John 3:16, "believe" is in the present tense. It's a present, active, participle, to be exact. ("Believe", when used as a present, active, participle, is synonymous with "faith", so this is "one who is being faithful".)
"Should not perish" is subjunctive. It might or might not happen.
So, the one believing might or might not perish.
Only one who has a life to lose can perish.
So, does that mean that the one who is believing, if he stops believing loses his spiritual salvation?
If so, why the contradiction with Acts 16:31?
How many contradictions are you willing to accept in Scriptures?
If you can't lose your spiritual salvation, then what does the one who stops believing lose?
It's also in the middle voice. He causes to happen for himself.
But, "have aionian life" is also subjunctive.
You can be faithful, and you can be having this life. (One Greek teacher that I know says that it describes a quality of life; not the adjective itself, but the concept.) But, it's not assured, because you can stop believing (stop being faithful), and you can perish. You can lose this aionian life, based on your actions.
If this is talking about being saved forever and ever, then it is based on your works, and you cause it to happen for yourself.
Is that what I must do to be saved forever and ever?