Isaac built an altar to God, offered sacrifices, and waited for Christ to come. (Gen. 26:25, Gen. 12:8, Gen. 13:4, Gen. 21:33)
Gen. 26:25 And he builded an altar there, and called upon the name of the Lord, and pitched his tent there: and there Isaac's servants digged a well.
Gen. 12:8 And he removed from thence unto a mountain on the east of Bethel, and pitched his tent, having Bethel on the west, and Hai on the east: and there he builded an altar unto the Lord, and called upon the name of the Lord.
Gen. 13:4 Unto the place of the altar, which he had make there at the first: and there Abram called on the name of the Lord.
Gen. 21:33 And Abraham planted a grove in Beersheba, and called there on the name of the Lord, the everlasting God.
The Old Testament prophesied that those who call on the name of the Jehovah will be saved. (Joel 2:32)
Joel 2:32 And it shall come to pass, that whosoever shall call on the name of the Lord shall be delivered: for in mount Zion and in Jerusalem shall be deliverance, as the Lord hath said, and in the remnant whom the Lord shall call.
To call on the name of Jehovah is to believe that Jesus is the Christ and to call on Jesus as Lord. Those who call on Jesus as Lord will be saved. (Romans 10:13, Acts 2:21)
Romans 10:13 For whosoever shall call upon the name of the Lord shall be saved.
Acts 2:21 And it shall come to pass, that whosoever shall call on the name of the Lord shall be saved.