Jamieson, Fausset and Brown on Joel 2:32

32. call on ... name of ... Lord--Hebrew, Jehovah. Applied to Jesus in Ro 10:13 (compare Ac 9:14; 1Co 1:2). Therefore, Jesus is Jehovah; and the phrase means, "Call on Messiah in His divine attributes."

shall be delivered--as the Christians were, just before Jerusalem's destruction, by retiring to Pella, warned by the Saviour (Mt 24:16); a type of the spiritual deliverance of all believers, and of the last deliverance of the elect "remnant" of Israel from the final assault of Antichrist. "In Zion and Jerusalem" the Saviour first appeared; and there again shall He appear as the Deliverer (Zec 14:1-5).

as the Lord hath said--Joel herein refers, not to the other prophets, but to his own words preceding.

call--metaphor from an invitation to a feast, which is an act of gratuitous kindness (Lu 14:16). So the remnant called and saved is according to the election of grace, not for man's merits, power, or efforts (Ro 11:5).