Charles Jennins (likely a believer) wrote the text for Messiah-Handel (not a believer) was commissioned to write the music for Messiah.
Handel donated much of his time and money to the needy, talked about God's guidance during a sword fight, maybe he was a deist or maybe a believer who lived for himself and not the Lord? He did not show a Christ-like attitude in his behavior with people, had many arguments with his singers, had a hot temper, was known to go into long bouts of depression, liked to consume lots of food and drink, swore like a sailor in three different languages, boastful.
Handel was the king of opera and had made most of his money from opera.
Handel was hesitant to give up Italian opera even when he began to lose money on it. His opera company suffered great financial loses but still he churned out new operas adding ballet and hoping the public would have a change of heart. When it didn't, he gradually became depressed and reclusive, strolling the dark streets at night and remaining locked inside his house during the day.
Eventually his health began to suffer. After a minor stroke and a mental collapse, he took a short leave of absence and traveled to a French spa where he hoped to be revitalized by the waters. It seemed to work.
Handel returned with renewed energy but once again he applied that energy to opera. His last two operas had only three performances, finally he had to surrender to the truth-opera was out.
Now in his 50s, Handel began to think more and more about working in other forms-especially the English oratorio. He sometimes used English writers for his inspiration, including the poet John Milton.
When he was 56 Handel decided to concentrate fully on oratorios and give up opera all together. (at that time, oratorios were often biblically based.) Handel's decision to write oratorios came in part from an invitation from the Duke of Devonshire who was the King's representative in Ireland. The Duke asked Handel to compose something for Dublin for a benefit for the poor. The assignment was just what Handel needed to bring him out of his doldrums and help get over his attachment to the unpopular Italian opera form.
Handel responded to the Duke by promising an oratorio. The oratorio he said would be called Messiah. He already had the idea for Messiah because his friend Charles Jennins had given him the script (or labreto) for it. Now he would create the music. Although most of Handel's oratorios were based on stories from the Bible, Messiah is an exception. It was based solely on quotations.
These quotes were gathered from the Bible by Handel's friend Charles Jennins and then Handel chose the ones that worked best with the music. Messiah contains no story or dramatic action, but through the quotes, Handel illustrated the founding of Christianity in songs that tell of the prophecy of Christ's coming, his birth, his life, death and resurrection. He said it was easy that Jennins had chosen quotes and put them in such an order that they were musical to begin with.
In all his future correspondence with Jennins, Handel always referred to his masterpiece as "Your Messiah.'