“Ye are of God, little children, and have overcome them: because greater is he that is in you, than he that is in the world.”  
1John 4:4

So many wonderful truths pointed out very loudly in the main verse:
He tells us our origin, Jesus has said:
“They are not of the world, even as I am not of the world.”  John 17:16
Now he tells us where we are of- we are of God.
“Sanctify them through thy truth: thy word is truth.”  John 17:17
He emphasized that since we were not of this world, the things of the world had no effect on us, now that we know we are of God, the only situations capable of moving us are those that move God.
In the main verse he explains to us that we have overcome them- the spirits of antiChrist.

“For many deceivers are entered into the world, who confess not that Jesus Christ is come in the flesh. This is a deceiver and an antichrist.”  2John 1:7

These are the spirits that put out thoughts and words that negate the salient truth that Jesus Christ came in the flesh; that divinity could tabernacle in flesh- as an extension, that it is possible to live the divine life of the earth, a life without sickness and all the uncertainties of the human nature, he says these spirits that work overtime to oppose these truths- we have overcome!
They are deceivers, they truly to ridicule and count as untrue that it is possible for divinity to be expressed fully on the earth by Jesus or by us- but we cannot be deceived, when we say we don’t fall sick, we have escaped their deception- we have overcome!

Irrespective of the problem- God says he- the expressions of the divine life- is greater in you than the problem could ever be, truly what is in you is far different from what is in the world, others have “antibodies”, we have the Holy Ghost and he is greater than all. Cheer up!