They triumphed over him by the blood of the Lamb and by the word of their testimony

Revelaton 12:1-17

Then another sign appeared in heaven: an enormous red dragon with seven heads and ten horns and seven crowns on its heads. Its tail swept a third of the stars out of the sky and flung them to the earth. The dragon stood in front of the woman who was about to give birth, so that it might devour her child the moment he was born.

She gave birth to a son, a male child, who “will rule all the nations with an iron scepter.” And her child was snatched up to God and to his throne. The woman fled into the wilderness to a place prepared for her by God, where she might be taken care of for 1,260 days. (About 3.5 Years)

Then war broke out in heaven. Michael and his angels fought against the dragon, and the dragon and his angels fought back. But he was not strong enough, and they lost their place in heaven. The great dragon was hurled down—that ancient serpent called the devil, or Satan, who leads the whole world astray. He was hurled to the earth, and his angels with him.

Then I heard a loud voice in heaven say: “Now have come the salvation and the power and the kingdom of our God, and the authority of his Messiah. For the accuser of our brothers and sisters, who accuses them before our God day and night, has been hurled down.

They triumphed over him by the blood of the Lamb and by the word of their testimony; they did not love their lives so much as to shrink from death.

Why?

There are wars between angels, including God's children and dragons; finally, the devil and dragon were cast out from heaven and defeated.

We are the rest of her offspring - those who obey God's commandments and hold to the testimony of Jesus.

How?

Keeping and honestly obeying God's commandments and holding to the testimony of Jesus is the way to eternal life.