The antecedents of all the pronouns in Isa 55 is defined in the first few verses:
1 “Come, all you who are thirsty, come to the waters; and you without money, come, buy, and eat! Come, buy wine and milk without
money and without cost! 2 Why spend money on that which is not
bread, and your labor on that which does not satisfy? Listen
carefully to Me, and eat what is good, and your soul will delight in
the richest of foods.
I think that Jesus may have had this passage in mind when He uttered the famous beatitudes, in particular Matt 5:3, 6:
3 “Blessed are the poor in spirit, for theirs is the kingdom of heaven.
6 Blessed are those who hunger and thirst for righteousness, for they will be filled.
Thus, Isa 55 and the beatitudes are a series of promises and blessings upon those who sense their great need, who "hunger and thirst for righteousness".
It is these who sense their need of Jesus, His grace and kindness, who understand something of their hopelessness, to whom Jesus gives good things. Isa has been a great source of comfort to those prepared to confess and partake of Christ's free offer of righteousness, 1 John 1:9.