John 14:12-14 describes NOT the core concept of Christianity.
It is this:
Jesus is the son of God.
He died, rose again to attain for our sins so that those that repent and believe in Jesus as their Lord and Saviour will be saved by the shedding of Jesus' blood. See John Chapter 3 which lays it out.
The power of God exists, as does the angelic power (both godly and fallen). The latter is better known as dark arts or magic, etc and it is very real. All eastern martial arts, Yoga, clairvoyance, Voodoo, Shamanism, etc are examples of these powers.
Back to Biblical truth: The main reason that this world is ruled by evil is that man has given authority to Satan to rule over humanity. (Gen 3:1, 6:1-4)
A quick look at what happened to the US
from June 7th 1963 when school prayer was removed demonstrates the concept.
A properly informed Christian will give Jesus authority over his life, thus having also authority over Satan and his agents.
Loving thy neighbors do NOT involve supporting or tolerating their efforts of theft, destruction, and murder. One prays that the enemy sees the light, so that they too may be saved.
Here is a two verses for the road:
Hosea 4:6
6 My people are destroyed for lack of knowledge: because thou hast rejected knowledge, I will also reject thee, that thou shalt be no priest to me: seeing thou hast forgotten the law of thy God, I will also forget thy children.
Proverbs 9:10
10 The fear of the LORD is the beginning of wisdom: and the knowledge of the holy is understanding.