“For nothing will be impossible with God.” Zechariah and Elizabeth are being paralleled with Abraham and Sarah. Here we have a direct allusion to Genesis 18:14, “Is anything impossible for the LORD? At the appointed time I will come back to you, and in about a year she [Sarah] will have a son” (HCSB). Earlier in the chapter we saw how Zechariah employed the same question as Abraham (see commentary on Luke 1:18; “sign”), and now this phrase originally regarding Sarah is applied to Elizabeth, who is barren and past fertile years. Like Sarah, she too will miraculously have a child. In Genesis the phrase was put as a question (expecting a negative answer), “Is anything impossible with the LORD?” (μὴ ἀδυνατεῖ παρὰ τῷ θεῷ ῥῆμα). Here in Luke it is as though the angel replies, answering in the future tense, “Nothing will be impossible with God” (οὐκ ἀδυνατήσει παρὰ τοῦ θεοῦ πᾶν ῥῆμα). This allusion would have been a great faith booster for Mary, who was about to have a child without sexual intercourse with a man.
Only the ASV prefers the translation, “For no word from God shall be void of power.” This is grammatically possible, and perhaps implied as a double meaning. Rather than simply “word,” the Greek word rhema (#4487 ῥῆμα) also means “thing, object, matter, event” (BDAG). Luke uses rhema to mean “thing” elsewhere: Luke 1:65; 2:15; 2:19; 2:51; Acts 5:32; 10:36.