THE TITLE "SON OF GOD":
In the Old Testament the title "son(s) of God" indicated a special relationship with the Almighty. The heavenly messengers [in Greek angelos] are called "sons" of God in Job 1:6, 2:1; 38:7. It was also a title given to a Judahite king at this enthronement [see Isaiah 9:5; Psalm 2:7; 89:27; 110:3] based on God's promise to David that his heir would be a "son" of God, beginning with Solomon [see 2 Samuel 7:14; 1 Chronicles 17:13]. It is for this reason that Jesus deserved the title "son" of God both in His divinity and in His humanity as the Davidic heir and rightful King of Israel. However, the chosen covenant people of Israel were also designated collective "sons" and "daughters" of God. In Exodus 4:22, Hosea 11:1, and in Jeremiah 31:20 the term "son" is used in the singular for the collective sonship of Israel and in Hosea 2:1, Isaiah 1:2, and Jeremiah 3:19 in the plural.
In the New Testament the title "Son of God" takes on a meaning not conveyed in the Old Testament. In the New Testament the title expresses a unique relationship with God as the Father's "only begotten son," Jesus of Nazareth. From the beginning this title characterized Jesus and His mission not only in the writings of St. John [1:14; 1:18; 3:16; 3:18 and 1 John 4:9] but also in the Gospel of St. Luke [see Luke 1:35] and the Gospel of St. Mark. In Mark 1:11 and 9:7 the title "Son" is revealed by God Himself. Demon spirits also divulge Jesus' title as divine "Son" in Mark 3:11 and 5:7. St. John declares that Jesus' title "Son of God" is the focus of the Jewish authorities' opposition to Jesus because it identifies His claim as the promised Messiah in John 5:18-20; 10:33; and 19:7. Jesus identifies those who make peace and those who love so genuinely as to offer God's love to their enemies as sons of God in the Sermon on the Mount in Matthew 5:9 and the Sermon on the Plain in Luke 6:35.
In the Gospels Jesus called God "My Father" [i.e. Matthew 10:32-33; 12:50; 16:17; 18:10, 19, 35; 26:39, 42, 53; Mark 14:36; Luke 10:21-22; 22:29, 42; 23:34, 46; John 5:17; 6:32, 44; 8:19, 38, 54; 14:28; 15:15; 20:17; etc.], but He distances Himself from the controversy surrounding the title "Son of God" until His trial before the Jewish Sanhedrin. He finally acknowledges His unique relationship to God as "Son" of the Father in the Gospels by quoting from the prophecy of the Davidic Messiah in Psalms 110:1 and Daniel 7:13-14, sending the High Priest into a rage [Matthew 26:63-66; Mark 14:61-62; Luke 22:68-71] that ends in Jesus' condemnation under the charge of blasphemy. But in the end, it is the Gentile Roman officer in charge of Jesus' crucifixion who announces to the world: "Truly this man was the Son of God" in Mark 15:39, a fulfillment of the prophecy that the Gentile nations would come to do homage to the promised Davidic Messiah! [see Isaiah 66:18-21; Ezekiel 34:13]. After His Resurrection His disciples recognized Him as Davidic Messiah and Lord and the true "Son of God." It is for this reason that His title as "Son" is primarily used by the Church after Easter for it is after His Resurrection and Ascension that Jesus is enthroned in the Heavenly Sanctuary as the "Son of God" and King of Kings: ...but in our time, the final days, he has spoken to us in the person of his Son, whom he appointed heir of all things and through whom he made the ages. He is the reflection of God's glory and bears the impress of God's own being, sustaining all things by his powerful command; and now that he has purged sins away, he has taken his seat at the right hand of the divine Majesty on high. So he is now as far above the angles as the title which he has inherited is higher than their own name. [Hebrews 1:2-4].