A.T. Robertson Commentary Luke 21:13

"It shall turn out unto you for a testimony." — Luke 21:13 (ASV)

It shall turn unto you (αποβησετα υμιν). Future middle of αποβαινω. It will come off, turn out for you (dative of advantage).

For a testimony (εις μαρτυριον). To their loyalty to Christ. Besides, "the blood of the martyrs is the seed of the church."