'Needs' in the Bible

Yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must ye needs go out of the world.

If someone thinks he knows something, he does not yet know to the degree that he needs to know.

But if all prophesy [foretelling the future, speaking a new message from God to the people], and an unbeliever or outsider comes in, he is convicted [of his sins] by all, and he is called to account by all [because he can understand what is being said];

For this corruptible must needs put on incorruptibility, and this mortal put on immortality.