From our Synod's website:
A singular prophet among the many in the Old Testament, Jonah the son of Amittai was born about an hour's walk from the town of Nazareth. The focus of his prophetic ministry was the call to preach at Nineveh, the capital of pagan Assyria (Jonah 1:1). His reluctance to respond and God's insistence that his call be heeded is the story of the book that bears Jonah's name. Although the swallowing and disgorging of Jonah by the great fish is the most remembered detail of his life, it is addressed in only three verses of the book (1:17; 2:1, 10). Throughout the book, the important theme is how God deals compassionately sinners. Jonah's three-day sojourn in the belly of the fish is mentioned by Jesus as a sign of his own death, burial, and resurrection (Mt. 12:39–41).
All the earth with joy is sounding:
Christ has risen from the dead!
He, the greater Jonah, bounding
From the grave, His three-day bed,
Wins the prize, Death's demise -
Songs of triumph fill the skies. LSB 462:1
O God, as the prophet Jonah spent three days in the belly of the great fish, so Your Son spent three days in the heart of the earth. Grant us repentance to embrace our death in Him through Holy Baptism and to proclaim His victory over sin and death to all the world; through the same Jesus Christ, our Lord. - Collect from the Vigil of Easter