The Church is the Body of Christ and consists of all those who have been saved by grace and washed in the blood of the Lamb. Since they are all in one Body, they will all be taken up at the Rapture at the same time. However, the ones who are watching for the the Blessed Hope of Christ coming for the saints, will also be the ones who will be prepared to go at any moment. And they will be living accordingly.
This passage in Matthew 24 must be interpreted properly:
37 But as the days of Noe [Noah] were, so shall also the coming of the Son of man be. 38 For as in the days that were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noe entered into the ark, 39 And knew not until the flood came, and took them all away; so shall also the coming of the Son of man be. 40 Then shall two be in the field; the one shall be taken, and the other left. 41 Two women shall be grinding at the mill; the one shall be taken, and the other left. 42 Watch therefore: for ye know not what hour your Lord doth come.
Even though it says in verse 39 that the Flood "took them all away" (meaning those who were not within the Ark), the Ark itself is a type of Christ. Those are in Christ are not subject to the wrath of God, therefore they will be taken out of the way before judgments come upon the earth. Therefore the ones who are "taken" in verses 40 and 41 are the saints of God (just like Noah). This also corresponds to the rescue of Lot and his family from Sodom just before divine judgments were poured out on Sodom and Gomorrah. And even before the Flood Enoch was taken by God (to prefigure the Rapture): And Enoch walked with God: and he was not; for God took him. (Gen 5:24)
It is significant to note that even though the family members of Noah and Lot are not called righteous, it was purely because Noah and Lot were deemed righteous that their families were saved from wrath. Today, those who have believed on the Lord Jesus Christ are deemed righteous by God. Which also means that God expects righteousness from them.