Revelation 12

⁷ And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels,

⁸ And prevailed not; neither was their place found any more in heaven.

⁹ And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.

¹⁰ And I heard a loud voice saying in heaven, Now is come salvation, and strength, and the kingdom of our God, and the power of his Christ: for the accuser of our brethren is cast down, which accused them before our God day and night.

¹¹ And they overcame him by the blood of the Lamb, and by the word of their testimony; and they loved not their lives unto the death.

¹² Therefore rejoice, ye heavens, and ye that dwell in them. Woe to the inhabiters of the earth and of the sea! for the devil is come down unto you, having great wrath, because he knoweth that he hath but a short time.

Revelation 20

And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand.

² And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,

³ And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that he must be loosed a little season.

⁷ And when the thousand years are expired, Satan shall be loosed out of his prison,

⁸ And shall go out to deceive the nations which are in the four quarters of the earth, Gog, and Magog, to gather them together to battle: the number of whom is as the sand of the sea.

⁹ And they went up on the breadth of the earth, and compassed the camp of the saints about, and the beloved city: and fire came down from God out of heaven, and devoured them.

¹⁰ And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever.

For example, when some sudden thoughts come to your mind, realise that it may sometimes be the thoughts or suggestions implanted into the mind by devil. Not all thoughts in our mind are the ones which originates from us.

To resist,

1. When some sudden unclean thought comes to mind, recognise the probability that the devil is trying to distract you.
2. After recognising this, refuse to think about that unclean thought. Purposefully distract mind to something positive or profitable.

God will definitely protect His children as per His will. The Bible makes it clear – Submit yourselves therefore to God. Resist the devil, and he will flee from you. – James 4:7 

God doesn’t say I will resist the devil for you. He asks us to resist the devil.

How would I know when to resist the devil?

New or old, every born again christian has the Holy Spirit dwelling within him. God commands us to resist satan clearly. So we should resist satan.

Submit yourselves therefore to God. Resist the devil, and he will flee from you. – James 4:7