Father Girardey gives a fifth reason why we ought to pray: because God expressly commands it.
“Luke, in his Gospel, writes that ‘Jesus spoke a parable (to teach us that) we ought always to pray and not to faint’ (Lk 18:1). On another occasion Jesus commands us to pray, saying: ‘Watch ye, praying at all times'; and why does He give us this command? That we may escape the snares in the road of salvation and ‘be accounted worthy to stand (at judgment) before the Son of man’ (Lk 21:36), and thus secure our salvation.”
“The Holy Ghost expressly commands us to pray, and to pray always, for He says in Holy Scripture: ‘Let nothing hinder thee from praying always’ (Sir 18:22), that is, we should let nothing prevent us from praying to God for His assistance in all our wants, as we learn from the commands God spoke through His prophets: ‘Cry to Me, and I will hear thee’ (Jer 33:3); ‘Call upon Me in the day of trouble, and I will deliver thee’ (Ps 49:15); ‘Seek ye the Lord, and be strengthened’ (Ps 104:4); that is, we should pray to God in our weakness, in time of temptation, or when we feel unable to perform what our duties or obligations require of us, and God will impart to us the strength we need.”
“Moreover, in doubtful or intricate matters the apostle bids us to pray, saying: ‘If any man want wisdom, let him ask of God, who giveth to all abundantly, . . . and it shall be given him’ (Jas 1:5).”
“Our divine Saviour expressly commands us to pray that we may avoid or overcome temptation: ‘Pray that you enter not into temptation’ (Mt 26:41).”
“Therefore, God wills that in all our wants we should pray to Him, and have recourse to Him for His help. And this is a strict injunction of Jesus Christ Himself: ‘Ask, and you shall receive; seek, and you shall find; knock, and it shall be opened to you’ (Lk 11:9).”
Quotations from Ferreol Girardey, Prayer: Its Necessity, Its Power, Its Conditions (St. Louis: B. Herder, 1916).