We are truly sorry to hear about your father's condition. Let's bring his needs before the Lord in prayer.
Before we pray, we would like to mention that Jesus tells us 'Ask, and it will be given you; seek, and you will find; knock, and it will be opened to you. For everyone who asks receives. He who seeks finds. To him who knocks it will be opened.' (Matthew 7:7-8 WEB). Notice that Jesus is saying that we need to be in a continual state of prayerful communication with God.
We are also told 'Let us therefore draw near with boldness to the throne of grace, that we may receive mercy, and may find grace for help in time of need.' (Hebrews 4:16 WEB). We need to come to the Lord in a state of boldness.
We are also told to pray that God's will be done. God does not always plan to heal everyone's body on this side of heaven. If this is the case, we can pray for other things such as a peace that surpasses understanding, the strength to endure, and for God's will to be done.
Let us pray.
Heavenly Father, we come before you in Jesus' name, pleading your will for this dear man's life. We ask, if it is your will, that you would bring healing to his body and relief from the pain and weakness caused by this hiatal hernia. If it is your plan to heal him through surgery, we pray for your guidance and wisdom for the medical team, and for your comfort and peace for him and the family during this time.
Lord, we also pray for his emotional and spiritual well-being. Please help him in his weakness and irritability, and fill him with your strength and patience. We trust in you, Lord, and we ask for your will to be done in his life. Draw him closer to you during this time, and help him to experience your unfailing love and faithfulness.
We ask this in the name of Jesus Christ.
In addition, make sure to pray in Jesus' name. God does not recognize our prayers if we do not pray in Jesus' name. Consider the following verses.
Jesus said 'Most certainly I tell you, whatever you may ask of the Father in my name, he will give it to you. Until now, you have asked nothing in my name. Ask, and you will receive, that your joy may be made full.' (John 16:23-24 WEB).
Jesus said 'Whatever you will ask in my name, that will I do, that the Father may be glorified in the Son. If you will ask anything in my name, I will do it.' (John 14:13 WEB).
In addition, Jesus said 'I am the way, the truth, and the life. No one comes to the Father, except through me.' (John 14:6 WEB).
This means that Jesus is the only way to God. There is no other way to approach God the Father. Not even through an angel, saint, or Mary. Make sure to pray in Jesus' name.