Jesus’ most commonly used title for Himself was “Son of Man.,” but the the most common title for Jesus in the New Testament is the “Son of God.” It was used by almost everyone who knew, or came to realize, who He was. The angel announcing His coming said He would called “the Son of God” (Lk. 1:35). John the Baptist testified to it (Jn. 1:34). Nathanael confessed it early on (Jn. 1:49) and Martha confessed in the cemetery (Jn. 11:27).
Jesus using called Himself the “Son of God” (Jn. 10:36), admitted to it when asked (Lk. 22:70) and was well-known for claiming it (Mt. 27:43). It was used by the devil and demons (Luke 4:3;41). The Jewish leaders demanded He admit to it so they could charge Him (Mt. 26:63), yet the centurion at the crucifixion concluded He truly was (Mk. 15:39).
The resurrection powerfully showed it was true (Rom. 1:4), and it is what believers preached (2 Cor. 1:19) and confessed (Acts 8:37; 1 Jn. 4:15). Him being the “Son of God” is the faith by which we live (Gal. 2:20) and in which we hope for eternal life (1 Jn. 5:13).
As the apostle John concluded his first letter: “And we know that the Son of God has come, and has given us understanding so that we may know Him who is true; and we are in Him who is true, in His Son Jesus Christ. This is the true God and eternal life” (1 Jn. 5:20).