John begins to describe a vision of 144,000 servants of God who become marked with seals. Their marking takes place after the Lamb opens the sixth seal and before he opens the seventh seal.
# the four corners of the earth
The earth is spoken of as if it were flat and square like a sheet of paper. The phrase "the four corners" refers to the north, south, east, and west.
# the seal of the living God
The word "seal" here refers to a tool that is used to press a mark onto a wax seal. In this case the tool would be used to put a mark on God's people. AT: "the marker" or "stamp" (See: [[rc://en/ta/man/translate/figs-metonymy]])
# put a seal on the foreheads
The word "seal" here refers to a mark. This mark shows that the people belong to God and that he will protect them. AT: "put a mark on the foreheads" (See: [[rc://en/ta/man/translate/figs-metonymy]])