Throughout the Old Testament there are many different names given to God, the most popular being Yahweh or “LORD” (used 6,800 times) followed by Elohim or “God” (used 2,500 times). But Jesus liked to use the word Patēr or “Father” in reference to God, which as R.T. France points out, “was distinctive of him, not a matter of general Jewish piety at the time” (The Gospel of Mark: A Commentary on the Greek Text, New International Greek Testament Commentary).
But while this was distinctive of Jesus, it wasn’t entirely new with Him. The analogy of God as Father and Israel as His children is found throughout the Old Testament, but it wasn’t a common title given to God on a regular basis. Yet that’s the key descriptive title that Jesus wants us to hold onto. For Him, God is “Our Father in heaven” (Matthew 6:9), and He instructed us to pray through that lens.
Of course this is difficult for some as not everyone has had a good father. Some of us have been abused by our dads in some way or have felt generally unloved by them. Others of us have had great fathers and for that reason have no problem calling God, “Father.”
But the Father that Jesus describes is unimaginably better than both the worst and best earthly Fathers we know and Jesus tells the story of the prodigal son to illustrate that. You could run away and offend God in every way possible, but if you return to Him, He’ll embrace you and throw a party. That’s not any earthly father I know—that’s not me as a father. But that’s what the perfect heavenly Father looks like.
Calling God a Father is an intimate way of referring to Him, and a lot of us are afraid to embrace that kind of intimacy, because like the prodigal son we don’t feel worthy of that kind of relationship. But Jesus understood God to be so intimate of a Father that while suffering with the choice to pursue the cross, He went so far as to refer to Him as “Abba,”
an Aramaic word…. meaning father or daddy. The word was used primarily by little children within the family circle. There is no evidence that Jews used the word in addressing God. Such familiarity, they thought, would be irreverent. By using the word, Jesus affirmed his intimate relationship with God. By commending it to his disciples—it is the Aramaic word that lies behind the Greek patēr in Matt 6:9; Luke 11:2—he affirmed that they could enjoy a similar relationship.James A. Brooks (Mark. The New American Commentary.)
The title “Abba” only appears two other times in the Bible, specifically in Paul’s writing. He uses it in exclamations of what joy Christians have in their adoption as children of God. So may we, too, take joy in our intimate familial relationship with God.