‘And he said to me, “O Daniel, you man greatly beloved (valued, precious), understand the words that I speak to you and stand upright. For I am now sent to you.” And when he had spoken this word to me, I stood, trembling.'
Notice that the standing upright and the understanding of God's words through His messenger are linked, Compare Daniel 7:4; Daniel 8:18. Man was made upright at the same time as he was made in the image of God as a spiritual and moral being. The one symbolises the other. That is why the nations were wild beasts that went on all fours, whereas the people of God were represented as the son of man.
‘You man greatly beloved.' What a testimony to an old man. He was greatly beloved of God, precious to God, the highest accolade that a human being could receive.
‘Understand.' That is, ‘listen and comprehend'.
‘And when he had spoken this word to me, I stood, trembling.' Daniel responded to the man's demand, but did so fearfully and with trembling. The situation had resulted in him being filled with awe.