The oratorio is divided into three parts; the first is a musical journey through Isaiah's prophesies about the coming Messiah, Jesus' birth and early ministry. The second part covers Christ's death, resurrection, ascension, and the early ministry of the gospel. The third part deals with eternal life, the Day of Judgement, the final defeat of sin and death, and the glorification of the Lamb of God.
I've seen The Messiah in it's entirety several times- Symphony Nova Scotia performs it every Christmas season- but have never sung in it. I have sung in a mass choir which performed several selections from it... I confess that I teared up the first time we did the Hallelujah Chorus. It is truly an inspired composition. At the end of his manuscript, Handel wrote three letters: S.D.G., which stand for "Soli Deo Gloria" which means "To God alone the glory." I can think of no better coda.
Below is a selection from Part I of The Messiah, "Comfort Ye My People," a tenor solo taken from Isaiah 40:1-5:
2 Speak ye comfortably to Jerusalem, and cry unto her, that her warfare is accomplished, that her iniquity is pardoned: for she hath received of the Lord's hand double for all her sins.
3 The voice of him that crieth in the wilderness, Prepare ye the way of the Lord, make straight in the desert a highway for our God.
4 Every valley shall be exalted, and every mountain and hill shall be made low: and the crooked shall be made straight, and the rough places plain:
5 And the glory of the Lord shall be revealed, and all flesh shall see it together: for the mouth of the Lord hath spoken it.