Adam Clarke on 1 Thessalonians 5:10

Who died for us - His death was an atoning sacrifice for the Gentiles as well as for the Jews.

Whether we wake or sleep - Whether we live or die, whether we are in this state or in the other world, we shall live together with him-shall enjoy his life, and the consolations of his Spirit, while here; and shall be glorified together with him in the eternal world. The words show that every where and in all circumstances genuine believers, who walk after God, have life and communion with him, and are continually happy, and constantly safe.

The apostle, however, may refer to the doctrine he has delivered, 1Thes 4:15, concerning the dead in Christ rising first; and the last generation of men not dying, but undergoing such a change as shall render them immortal. On that great day, all the followers of God, both those who had long slept in the dust of the earth, and all those who shall be found living, shall be acknowledged by Christ as his own, and live together for ever with him.