Jonah 1:10–16 (NKJV)
10 Then the men were exceedingly afraid, and said to him, “Why have you done this?” For the men knew that he fled from the presence of the Lord, because he had told them. 11 Then they said to him, “What shall we do to you that the sea may be calm for us?”—for the sea was growing more tempestuous.
12 And he said to them, “Pick me up and throw me into the sea; then the sea will become calm for you. For I know that this great tempest is because of me.”
Jonah knew he was responsible for the disaster that was upon the ship. He had just in the last verse told them that he served the Lord and feared Him, and never denied his disobedience. Now, he takes responsibility for his sin and instructs them to exercise the death penalty against him to spare their own lives. He acknowledges that He has willfully sinned against God and submits himself for punishment. This is not a sacrifice to the sea, but rather a sacrifice to God for forgiveness and safety for the ship.
13 Nevertheless the men rowed hard to return to land, but they could not, for the sea continued to grow more tempestuous against them. 14 Therefore they cried out to the Lord and said, “We pray, O Lord, please do not let us perish for this man’s life, and do not charge us with innocent blood; for You, O Lord, have done as it pleased You.” 15 So they picked up Jonah and threw him into the sea, and the sea ceased from its raging. 16 Then the men feared the Lord exceedingly, and offered a sacrifice to the Lord and took vows.
The sailors did not want to exercise this kind of vigilante justice, and tried hard to row back to shore, to no avail. They asked God to spare them from Jonah’s punishment, and not to punish them for killing him, either. Then they threw him overboard, feared the Lord, and offered a sacrifice of their own to Him.
What has happened here is that Jonah confessed his sin and offered himself as a sacrifice. Get the sinner out of the boat, he suggests. Whether he repented yet or not is not clear. Perhaps the next phase of his journey was necessary for that to happen (or maybe the phase after that). However, the understated result was that a crew of sailors came to know and understand a bit about Yahweh, the true God, the God of Heaven. We never know what our sacrifice may effect in our lives and the lives around us. I do not believe human sacrifice is a viable method of witnessing today, but the sacrifices we make for the cause of Christ, the piety, the dedication all mean something in the scheme of salvation. Give in order to save: that is sacrifice of a noble and holy kind.