In the Old Testament God is not that often spoken about as father. God is described as a king, lord, mighty one and so on. When God is spoken about as father he is usually depicted as the father of the Jewish people and nation.
However, things changed drastically in the New Testament times. Jesus frequently addresses and speaks about God as father. The Aramaic word (at this time the Jews did not speak Hebrew. Hebrew was for scripture and liturgy, but they spoke Aramaic) is “Abba”. This is an unusual use of the word. Usually, when a Jew prayed to God as father he used a somewhat more formal term. Sometimes it is said the word “Abba” means “daddy”, but that is not quite the case because it is no childish word.
Rather it indicates a strong, mature love between Jesus and his Father. Abba is a word of deep intimacy and this is the usual way Christ addresses God. And, as far as we know, Jesus was the only Jew on record speaking to God in this way. Others did not, so the use of this word is one of the indications that Jesus thought of himself as the son of God in a unique sense. Sometimes it is said that Jesus did not claim explicitly to be God (except in the Fourth Gospel), but Jesus ‘ use of this word is an example of his having a unique relationship with God.
It should be noticed that in speaking to the apostles he never referred to God as “Our Father” but always made a distinction between how Jesus viewed God in relation to him and to his apostles. Some will object and say that Jesus taught his disciples the Our Father. This is true. However, it is not really an exception. When Jesus Christ was teaching them this prayer he was speaking as one of the apostles In effect, he was teaching a liturgical form rather than speaking to his Abba personally. An example of this way of speaking is found in Christ’s words to Mary Magdalen after his resurrection:
“I am ascending to my Father and your Father, to my God and your God.” (Jn 20:17)
To sum up, Jesus’ use of the word Abba to address God shows Jesus’ sense of having a uniquely intimate relationship with God.
However, Jesus did teach his apostles the “Our Father”. This shows that through our Christian faith we become sons and daughters of God. We never become God in substance, but by grace. We become sons and daughters of God through baptism.
Baptism is our “adoption ceremony” so to speak. As St. Paul writes in his letter to the Galatians (Gal 4:4-7): “But when the fullness of time had come, God sent his Son, born of a woman, born under the law, in order to redeem those who were under the law, so that we might receive adoption as children. And because you are children, God has sent the Spirit of his Son into our hearts, crying, ‘Abba! Father!’ So you are no longer a slave but a child, and if a child then also an heir, through God.”
We can see why Jesus gives us the parable of the Prodigal Son. The young man takes his father’s money and wastes it in riotous living in a far country. When he is completely out of money he realizes what he has done and decides to go back to his father and ask him to hire him as his servant. However, the father rejoices to see himand forgives him. This parable, of course, is for us. Through the sins we have committed we have distanced ourselves from God, but God is waiting for us to come back to Him. And the way we do this is through baptism, in which we participate, in a certain sense, in Jesus Christ’s “Abba” experience.