While it is true, the church is spiritual Israel, it is not true that spiritual Israel has twelve tribes. On the other hand, suppose John intended to inform us of the sealing of God's servants from under the Old Testament system. This not only fits the teaching of the rest of the Bible but it is what John said. To ignore this plain statement in favor of some other glorified explanation testifies that the expositor misunderstands and misapplies this scene. In chapter thirteen, John identifies the sea beast by a number.
Many expositors understand the sea beast represents the Roman Empire.
We do not need to know the number of the beast to conclude this. We conclude this from the context. Commentators often view the number 666 as symbolic of imperfection and conclude it applies to the Roman Empire to show that it does not measure up to God whose number is the perfect 777. To be frank, I could tell that about this beast if John had never confused me with the number. It has long been recognized that 666 is the number of Nero's name.