What is commonly referred to as the Lord’s prayer is actually the disciple’s prayer.  Jesus is instructing His disciples on how to pray in Matthew 6.  The Lord’s prayer, His intercession for His disciples and for us, is found in John chapter 17.

And when thou prayest, thou shalt not be as the hypocrites are: for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, they have their reward. But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly. But when ye pray, use not vain repetitions, as the heathen do: for they think that they shall be heard for their much speaking. Be not ye therefore like unto them: for your Father knoweth what things ye have need of, before ye ask him. After this manner therefore pray ye:  Our Father which art in heaven….

Who can say God is my father?  God is the father of all those who have been born again.  This is a spiritual birth.  Everyone has been born physically, but those who have repented (changed their minds) and believed in the death, burial, and resurrection of Jesus Christ, by grace through faith, have been born again.  Jesus explained in John chapter 3 that unless one is born again, he or she cannot see the kingdom of God.  I Peter 1:23 states it this way; Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth forever.  Romans 10:17; So then faith cometh by hearing, and hearing by the word of God.

Some believe that God is the father of all mankind and in a sense, as Creator of all, He is. But Jesus made a distinction when He addressed the religious leaders of His day.  Jesus said; Ye are of your father the devil and the lusts (desires) of your father ye will do (John 8:44).  Again, in the same chapter Jesus declares; He that is of God heareth God’s words: ye therefore hear them not, because ye are not of God (John 8:47).  God is not the father, therefore, of those who will not hear His Word.

On the other hand; But as many as received him (Jesus Christ), to them gave he power to become the sons of God, even to them that believe on his name: Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.  John 1:12&13

And because ye are sons, God hath sent forth the Spirit of his Son into your hearts, crying, Abba (papa), Father.  Galatians 4:6

…let the word of Christ dwell in you richly…