Lord Jesus said the gate to life is narrow, and the road to it is difficult. Why did He say so?
Because narrow is the gate and difficult is the way which leads to life, and there are few who find it. Matthew 7:14
It is because there is only One Way to Life, and all the rest (which are many) can only lead to destruction. Similarly, there is only One True God, and all the many others who call themselves gods are merely deceivers.
Which Way is the Way to Life?
In John 14:6, Jesus made it very clear that He is the only way to life. He is also that Gate of the sheep, and only those who enter through Him can be saved.
Jesus said unto him, I am the way, the truth, and the life. No man comes unto the Father, but by me. John 14:6
What and Where is the Gate?
Then said Jesus unto them again, Verily, verily, I say unto you, I am the gate of the sheep. All that ever came before me are thieves and robbers: but the sheep did not hear them. I am the gate; by me if any man enter in, he shall be saved, and shall go in and out, and find pasture. John 10:7-9