1)
What is the meaning of "va'Ysirehu Sha'ul me'Imo"?
1.
Radak: He arranged that he not be in the house constantly, like before. Rather, he will go in front of the nation.
2.
Malbim: He demoted him, that he will not be so close to the king, and now he will be the general only over 1000 (before, he was the head general over the entire army - verse 5).
2)
Why does it say "he left and came in front of the nation"?
1.
Malbim: Even though Sha'ul tried to demote him, it did not help. The nation did not do anything without him!