What does Daniel 1:21 mean?

God gave Daniel a lengthy ministry. His service as a faithful representative of the Lord extended from Nebuchadnezzar to King Cyrus of Persia. By divine grace, Daniel lived and ministered throughout the reigns of Nebuchadnezzar in 604—562 BC, Evil-Merodach in 562—560 BC, Neriglissar in 560—556 BC, Labashi-Marduck in 556 BC, the co-rules of Nabonidus in 556—539 BC and Belshazzar in 553–539 BC (Daniel 5:1), and into the reign of Cyrus the Great of Persia.

In His providence, God also favored the Israelite patriarch Joseph with a long stretch of influence in Egypt. His ministry began at age thirty in Pharaoh's court and continued until he died at the age of 110 (Genesis 41:46; 50:22). Daniel's ministry to the Gentiles foreshadowed a prominent New Testament figure, who lived into his nineties and faithfully proclaimed God's Word. This was John, one of Jesus' original disciples. Apparently, the Romans thought that by banishing John to the isolation of Patmos they would silence him. Yet, from Patmos, John wrote the Revelation of Jesus Christ that promises blessing to whoever reads it, to whoever hears it, and to whoever obeys it (Revelation 1:3).