The sending of Jesus Christ into the world - both as a means of self-revelation and as the means of redemption for the world - was part of God's plan and not a reaction to unforeseeable events (Romans 5-6, Galatians 4.4). Before the foundation of the world, God fully intended to send his Son to earth as his means of redeeming creation (Galatians 4.4, John 3.16). Jesus' purpose in his earthly life was to be obedient to all that his Father commanded him to do (John 4.34, Romans 5.18-29), fulfilling all Old Testament prophecies concerning the Messiah (Psalm 22.1, Isaiah 7.14, 53.5-12, etc.).
The Humanity of Christ - In his incarnation, Jesus took on a fully human form (Philippians 2.6-8, Hebrews 2.17), being born of Mary and conceived by the Holy Spirit (Luke 1.34-35). Jesus became fully man, while yet remaining fully God (Luke 2.52, Philippians 2.6-7). Being fully human Jesus therefore experienced human emotion, was subject to human needs (hunger, thirst, physical pain, etc.), suffered the effects of living in a sinful, fallen world, and even faced the temptations of such a world, but remained without sin (Matthew 4.1-2, 6, 19.34, Hebrews 4.15).
The Deity of Christ - Although he was fully human, Jesus is also fully God, a combination which remains a mystery to the natural mind (John 1.1). We know, however, that Jesus was indeed fully human yet fully God through severe set of biblical data: he claimed to be divine (Matthew 11.27); he provided evidence of his divine nature through miraculous works and deeds (John 14.9, Matthew 4.23-24); he taught as one with divine authority, such as had never been heard before (Mark 1.22); his knowledge of future events (Luke 9.22); his glorification (Luke 9.18-36); his ascension; his power over demons (Mark 5.1-13), etc.
The Atonement - The atonement refers to that work of God whereby the debt of sin was canceled through the death of Christ on the cross (Ephesians 1.7, Colossians 1.14). In so doing, God satisfied the just requirement of his holy wrath and accomplished salvation for all those who would believe (Galatians 3.13, Romans 5.9). The death of Christ was necessary for the sake of satisfying God's justice, as he could not let sin go unpunished (1 Peter 3.18). Through the atonement, the sins of all those who would ever believe were paid for, and Christ secured their salvation, interceding on their behalf (Hebrews 4.14, 9.24).