I view the 144,000 Israelites in Rev 7:4–8 as sealed in the sense of God choosing them to be saved when the end of the seven-year period is completed, fulfilling Daniel’s 70 week prophecy of the nation of Israel when they recognize Jesus as Messiah. They are also sealed in the sense of protection from the impending wrath of God (cf. Rev 9:4!) via the trumpets and bowls judgments.
Some rather have claimed the 144,000 are saved at the moment they are sealed because they are described as “bond-servants.” However, as Robert Gundry has pointed out, this is not a necessary conclusion: “The designation ‘bond-servants’ (7:3), then, anticipates their role in the reestablishment of the Davidic kingdom. Isaiah calls unregenerate Israel the ‘servant’ of the Lord (42:18–25) in anticipation of the nation’s restoration (43:1ff.)—exactly the interpretation here given for the 144,000 [see also similar anticipatory statements in, for example, Jer 1:5; Luke 1:15]” (The Church and the Tribulation, 82).