The 144,000 may have been tasked with evangelizing the earth, but there is nothing in the text of Revelation that would suggest this. Certainly, there is no literary tie between the 144,000 and the multitudes of saints that came out of the Tribulation in Revelation 7:9, 10. Both of these groups are in Heaven - the 144,000 are being sealed in Heaven and the and now found in Heaven being comforted by God but there is nothing in the text that connects the two of them.
We see the Two Witnesses prophesying in Revelation 11:6 and the angel in Rev 14:6 having the eternal gospel to preach, so if the 144,000 were evangelists, why doesn't the text say so?
What do we know about the 144,000?
1) They are saved from among the lines of Israel as the text so clearly states in Revelation 7:4-8. Those in the replacement theology camp are uncomfortable with this idea so they attempt to allegorize and spiritualize this passage away, but the fact is that God still has a plan for the people of Israel.
2) They were sealed in Heaven Rev 7:1-4 as the whole drama of Rev 7 takes place in Heaven, suggesting they are resurrected, and glorified saints. Perhaps because you may be in the pre-trib rapture camp that you cannot reconcile a part of the church being on the earth. However, these are resurrected and glorified saints so even within the pre-trib construct, they can. Perhaps the most compelling reason to believe that these 144,000 were resurrected and glorified saints is they were described in Rev 14:4 as: "These are the ones who have not been defiled with women," contrasting them to the 200 falling angels in the Book of Enoch who united with women and created the Nephilim. We find in Rev 14:4 that they had been "purchased from the earth", and finally, they are defined as "the first fruits of God" Rev 14:4 which connects them with the resurrection imagery of the Feast of First Fruits.
3) The 144,000 are sealed with the name of the Father and the Son, partially as you suggest to protect them. As the righteous were protected in Ezekiel 8 - 9, by being sealed with a Tev, or a cross as it would have been marked in Ancient Hebrew, so the 144,000 come under the authority and atoning blood of Messiah. But there is more to this sealing than just coming under the protection of the upcoming judgment, as the seal of 144,000 is being contrasted here in chapter 14 with the seal of those who were marked by the beast in chapter 13. As those who followed the Beast were able to buy or sell because of their mark, the 144,000 were connected to God through their seal for their provision and power.
4) What we do know that the 144,000 did, was worship! Revelation 14:3 says "They sang a new song before the throne and before the four living creatures and the elders, and no one could learn the song except the one hundred and forty-four thousand." There are 10 celebrations of worship in the Book of Revelation and after each celebration, something amazing happens. In this case, the worship of the 144,000 evokes the rapture of the church in Revelation 14:14-20. I also believe they are part of the worship celebration of Revelation 15, as "they sang the song of Moses, the bond-servant of God, and the song of the Lamb" - something you could imagine a group of redeemed and glorified Messianic saints could do. In the celebration of worship of Revelation 15, they bring about the the anti-creation event of Revelation 16.
We see the Two Witnesses prophesying in Revelation 11:6 and the angel in Rev 14:6 having the eternal gospel to preach, so if the 144,000 were evangelists, why doesn't the text say so?
What do we know about the 144,000?
1) They are saved from among the lines of Israel as the text so clearly states in Revelation 7:4-8. Those in the replacement theology camp are uncomfortable with this idea so they attempt to allegorize and spiritualize this passage away, but the fact is that God still has a plan for the people of Israel.
2) They were sealed in Heaven Rev 7:1-4 as the whole drama of Rev 7 takes place in Heaven, suggesting they are resurrected, and glorified saints. Perhaps because you may be in the pre-trib rapture camp that you cannot reconcile a part of the church being on the earth. However, these are resurrected and glorified saints so even within the pre-trib construct, they can. Perhaps the most compelling reason to believe that these 144,000 were resurrected and glorified saints is they were described in Rev 14:4 as: "These are the ones who have not been defiled with women," contrasting them to the 200 falling angels in the Book of Enoch who united with women and created the Nephilim. We find in Rev 14:4 that they had been "purchased from the earth", and finally, they are defined as "the first fruits of God" Rev 14:4 which connects them with the resurrection imagery of the Feast of First Fruits.
3) The 144,000 are sealed with the name of the Father and the Son, partially as you suggest to protect them. As the righteous were protected in Ezekiel 8 - 9, by being sealed with a Tev, or a cross as it would have been marked in Ancient Hebrew, so the 144,000 come under the authority and atoning blood of Messiah. But there is more to this sealing than just coming under the protection of the upcoming judgment, as the seal of 144,000 is being contrasted here in chapter 14 with the seal of those who were marked by the beast in chapter 13. As those who followed the Beast were able to buy or sell because of their mark, the 144,000 were connected to God through their seal for their provision and power.
4) What we do know that the 144,000 did, was worship! Revelation 14:3 says "They sang a new song before the throne and before the four living creatures and the elders, and no one could learn the song except the one hundred and forty-four thousand." There are 10 celebrations of worship in the Book of Revelation and after each celebration, something amazing happens. In this case, the worship of the 144,000 evokes the rapture of the church in Revelation 14:14-20. I also believe they are part of the worship celebration of Revelation 15, as "they sang the song of Moses, the bond-servant of God, and the song of the Lamb" - something you could imagine a group of redeemed and glorified Messianic saints could do. In the celebration of worship of Revelation 15, they bring about the the anti-creation event of Revelation 16.