I teach science, and one of subjects I teach is modern Physics. So I teach about Black holes. I recently came across a YT video, "Astrophysicist Explains Black Holes in 5 levels of Difficulty (Child, Teen, College Student, Grad Student, Expert)".
It points out that in order to explain something to someone, you need to know who your audience is, and you have to have some idea of their previous knowledge.
I approach the gospel in the same way.
You can explain what the gospel is in MANY different levels of expertise. Usually, if we are evangelizing, we assume no prior knowledge, and so we present it in its simplest form:
1) God is holy;
2) Man has sinned;
3) The wages of sin is death;
4) All men are condemned to death for their sins.
5) God chose to be merciful, and sent His son to die to atone for sin.
6) If you believe in God's son Jesus Christ, you will be saved.
But you can go into more detail:
1) What is sin? This is why Ray Comfort's approach is to appeal to the Ten Commandments and to personal experience;
2) Where did sin come from?
3) What does "death" mean?
4) Who is God's son?
5) Did God's son need to be perfect?
6) Did God's son need to be God?
7) What does it mean to "believe"?
8) Where does "belief" come from?
9) How do faith and works relate to one another?
10) etc.
11) etc.
12) etc.
And so on, and so on...
So depending on your audience and your intended comprehensiveness, you can present the gospel on a tract the size of a credit card, or you may fill a 300+ -page book.
I don't believe Spurgeon (and he is the ONLY one they can find to depend on this "quote") was saying that if an Arminian presents the gospel without appealing to Calvinism, or that if he includes the prescription of "free will", that it wasn't the gospel.
I believe Spurgeon's only point was that if you take the gospel to its most complete and comprehensive end, what you end up with is "Calvinism".
Which makes the poster's repeated criticism a worthless joke.