Return you double

In The Book of Zechariah, Chapter 9 Verse 12 states:

 In the return to the fortress of the waiting prisoners,      
 This very day, I will return you double for your exile.       

Please explain about the exiles and return double. 

From the Haydock Commentary:

Ver. 12. Hold. Return ye, who stay behind, to Jerusalem. God will make good all that you abandon; or come, Judas has procured liberty for the people, 1 Machabees iv. 36. (Calmet) — Embrace the gospel, and enter the Church. (Menochius)

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