The people of the Exodus and some prophets of Israel were at ease regarding themselves collectively as God's sons (in effect God's children), and God as their father,
'Then you shall say to Pharaoh, 'Thus says the Lord, "Israel is My son, My firstborn. "So I said to you, 'Let My son go that he may serve Me' (Exodus 4:22)
'Look down from heaven and see, and take care of this vine, even the shoot which Your right hand has planted, And on the son whom You have strengthened for Yourself.' (Psalm 80:14-15)
'Listen, O heavens, and hear, O earth; For the Lord speaks, "Sons I have reared and brought up, But they have revolted against Me.' (Isaiah 1:2)
When his contemporaries heard Jesus speak of his intimate relationship with his Father, they regarded him as going beyond how they thought about themselves in relation to God to the point of blasphemy.
He quotes to them verse six of Psalm 82, somewhat provocatively, as the Psalm is about divine moral judgement against lesser divinities, exercised by the one who is 'A great king above all gods' (Psalm 95:3b), and Author of the Law. These gods do not inhabit eternity, but are mortal, for they are projections of human imagination and ignorance.
'They do not know, neither do they understand; They walk about in darkness; All the foundations of the earth are shaken. I said, "You are gods, And all of you are sons of the Most High. Nevertheless you will die like men And fall like any one of the princes."…' (Psalm 82:5-7)
What is said of lesser divinities also applies to human beings. Yet despite being born to die, human beings are held in special regard, called to partake of divine life in eternity.
'What are human beings that you are mindful of them, morals that you care for them? You made them little lower than a god and crowned them with glory and honour.' (Ps 8:4-5)
For Jesus, whether anyone can truly be regarded as a son of God depends on whether or not they do the Father's work, keep his commandments, believe and trust in him. His critics see what he does and the way he does it, but find this too demanding of them challenging their actions and attitudes, and so they reject the evidence of his life, and end up denying any sense in which he could be regarded as like them, sons of the Most High.
Conscious of our faults and frailties, we come to prayer in humility, taking our confidence to approach despite our limitations God from St Paul's words
'For you are all children of God through faith in Christ Jesus. For all of you who were baptized into Christ have clothed yourselves with Christ.' (Galatians 3:26)
And from St John
'Beloved we are God's children now. What we will be has not yet appeared; but we know that when he appears we shall be like him, because we shall see him as he is.' (1 John 3:2)
This is a good and sufficient reason pray as Jesus taught us saying - 'Our Father ... '