Christ is the first begotten of God and created. He is in perfect communion with God and as such he is the Son of God. The title describes the intimate relationship he has with his Father. He is the closest to God, and has never sinned.
We also become Sons of God through the Christ. We believe that he works as a mediator between us and God and helps us on our journey to become divine, that is to avoid sin and be in harmony with God and our fellows. The title used to be called especially of the judges of Israel, who held a sort of a divine kingship. King David is held as a prefigure to Jesus, ruling with God's authority. This co-rulership alongside Jesus is promised to Christians as well, those who are the builders of God's kingdom here on earth.
Everyone has a divine spark, they couldn't be alive without it, but not everyone walks in the fullness of the spirit. This spirit means the active force of God that influences the world. Spirit is also a term for what God is, a sort of a term for the power of life and love. The spirit is a helping force that aids us to act justly and do our duties, makes us stronger, and to love our fellows. It's very mystical term, and so is hard to express in words.