There are many opposites in life.

• Good vs. Evil
• Rich vs. Poor
• Sickness vs. Health
• Birth vs. Death
• God vs. Devil
• Christ vs. Antichrist
• Free will vs. Predestination
• Electrons vs. Positrons
• Stars vs. Black Holes
• Positive vs. Negative
• Up vs. Down

The concept of some of the above is easier to grasp than of others.

The concept of good versus evil is fairly universally accepted.  Some things are good; some are bad.  Good is the opposite of evil and vice-versa. 

Of course, some things are sort of in between.  It is almost as though there is a continuous range with good on one end and evil (or bad) on the other end.
 
The line between good and evil is not a linear scale.  Nor, is there agreement on the "calibration" of the scale.  This results in many disagreements and other struggles between people.
 
Add to this the problem that something may be good for one person but bad for another.  (My loss is your gain.) 

I am ok with the basic concept of God.  I have a little more difficulty with the concept of the Devil.  Frankly, it is a bit too much for me when I start thinking about "Who created God?" let alone, who created the Devil.

So, having finite brain capacity, I just accept that there is a God.  (There has to be something we call whatever created the universe.)

People sometimes use the expression, "The Devil made me do it," to rationalize away bad behavior.  Interesting, we don't call them insane.  Whereas, if someone says, "God made me do it," we usually consider them to be completely nuts."

People have known about the stars for eons.  We can see the stars -- except where we have saturated the night environment with visual pollution (e.g., urban centers.)  If you or I point to a star, the other can agree that is a star.
 
On the other hand, who has actually seen a black hole? 
 
Even if we accept on faith the concept of black holes, the black hole is not exactly the opposite of a star.

Scientists now tell use that is matter and anti-matter.  Matter consists of neutrons, protons, and electrons.  They make up atoms, which make up molecules, which make up .... 
 
Anti-matter consists of positive-charged "positrons" (the opposite of negative-charged electrons and negative-charged "anti-protons" as the opposite of positive-charged protons.

I have never really understood the concept of the Antichrist. 

• Some say the Antichrist is the devil (and the opposite of God.)
• Some say the Antichrist is the counterpart of Jesus Christ.
• Some say the antichrist is anyone whom does not believe as they do.
• Some say the antichrist is anyone they hate.
• Some have said Hitler was the Antichrist.
• Then some said that Stalin was the Antichrist.
• Some even claimed that the Pope is the Antichrist.
• Now some say that President Obama is the Antichrist.  Aw, come on now folks.

I am more inclined to believe that Antichrist is the leader of the hate mongers.
(Or that the antichrist is any of the hate mongers out there, along with those who incite them.)