The characteristics mentioned in Daniel 1:4 are not unrelated. The boys who are chosen have to meet all these conditions. They are to be the strongest and smartest sons of the prominent families, showing a sense of responsibility. They have to be able to serve in the court of the Babylonian king and be able to fill responsible positions in this court later on.
Nebuchadnezzar knows very well that it is important for his kingdom that aspiring rulers leave their own culture, religion and language behind. For this reason he does everything he can to Babylonize
them. His intent is to secularize them entirely, to win these youths over to himself and to Babylon. These conquered youths are to learn the culture and customs of Babylon and by going through the king’s educational process to become leaders who will feel like true Babylonians. Even the youth of God’s people, the youth of the church, cannot escape this process.
These are fairly young boys, perhaps as young as fourteen years old, and at an age where they are open to a lot of influences. It is known that in these days at the Assyrian and Babylonian courts, boys started their education around this age and usually followed a three-year course. This corresponds to what we are reading here.
4 youths without blemish, of good appearance and skillful in all wisdom, endowed with knowledge, understanding learning, and competent to stand in the king’s palace, and to teach them the literature and language of the Chaldeans.