⁵ “Do not fear, for I am with you;
I will bring your offspring from the east,
And gather you from the west.
⁶ “I will say to the north, ‘Give them up!’
And to the south, ‘Do not hold them back.’
Bring My sons from afar
And My daughters from the ends of the earth,
⁷ Everyone who is called by My name,
And whom I have created for My glory,
Whom I have formed, even whom I have made.”

Isaiah 43:5-7 

Israel had fallen.  In another century, Judah would as well. Both would be in captivity. From Judah's fall, it would be another 70 years until God called His children to come back home. 

Though that time was yet almost two centuries in the future, Isaiah writes of the anticipation of the Lord to receive back His sons and daughters.  When that time comes, the Lord says, Do not hold back!" 

"Do not hold (them) back"  "Them" is actually supplied by the translator. It changes the meaning slightly. Either way: consider: 

If "them" is correct: Then this admonition is to the world: Do not inhibit or discourage those who hear and decide to respond to the Lord. Don't hold them back. 

If without the "them" is correct:: To the sons and daughters: "Come on home. Do not hesitate. Do not hold back.  It is the right thing to do. The Father is waiting for you." 

So which is it? Either way it is a powerful admonition and certainly both are valid concepts. I prefer to go with what the translators decided, but either way, it is something worth thinking about!