Who are the 144 thousand and why are they called the `First fruits` ?

These are they which were not defiled with women; for they are virgins. These are they which follow the Lamb whithersoever he goeth. These were redeemed from among men, being the firstfruits unto God and to the Lamb.  Rev 14 vs 4

Are they called the `First fruits` because, - all who have become born again Christians are called `first fruits`? Does this mean that the Bride of Christ will be raptured before the 144 thousand are raptured?

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Jane A