Matthew 4:17

Those who heard Jesus teach.

The object is unstated, but is presumably the message of Jesus, that the kingdom (and their King) are at hand.

The consequence for repentance or lack thereof is not expressed, nor may it be reasonably inferred with any certainty.

Matthew 12:41

Men of Nineveh

Matthew does not state the object of Nineveh's repentance, as it was not relevant to Jesus argument. However, a review of the Book of Jonah discloses that the object of repentance was the sin of violence and wickedness.  The Assyrians were known to skin their enemies alive during battle.

Matthew does not disclose the consequence of Nineveh's repentance, for it was not relevant to Jesus argument.  However, the Book of Jonah shows that their repentance resulted in their temporal deliverance.  God spared the city from temporal judgment.

Romans 11:29

God

The election of Israel

God will not repent.  Even though the Jews of Jesus day had rejected Jesus, the promises God made to Israel will be fulfilled.

Hebrews 6:6

A hypothetical believer who falls away from their Christian Faith.

The object of repentance is not expressly stated, but from the context, it appears to be identical to verse 1.  One must repent of dead works and trust in Christ alone to be saved.  One who falls away from the Christian faith unto a religion of salvation by ritual must be restored to the same faith by which he was saved.

Not stated in the immediate context.  The greater context of the entire epistle shows that one who falls away from his faith also walks away from his inheritance.  (The privilege of ruling and reigning with Christ, which is a reward for faithfulness to our Savior.)

Hebrews 7:21

The Lord

The appointing of Jesus as an High Priest after the order of Melchisedec (vs. 21).

Jesus will continue forever in an unchangeable priesthood (vs. 24).

Revelation 2:5 (2 x)

The church of Ephesus

They had "left their first love."  The context shows that they are clearly saved.

"I will come unto thee quickly, and will remove thy candlestick out of his place" (vs. 5). The nature of the judgment is poetic, but is plainly dealing with temporal judgment of the local church at Ephesus, not eternal judgment.

Revelation 2:16

The Church of Pergamos

The object(s) from which they are called to repent are the doctrine of Balam and the Doctrine of the Nicholatians.  Saving faith is not in view, since they are already said to hold fast His name.

Poetic language suggests that temporal judgment and eternal rewards are both in view.

Revelation 2:21 & 22

A false prophetess called "Jezebel" (vs. 20, 21), and they which commit adultery with her (vs. 22).

She is called to repent of "her fornication," and "they which commit adultery with her" are called to repent of their "deeds."  Although it may be metaphorical, there are reasons for interpreting the passage plainly.

She will be cast into a bed, and those that commit adultery with her into tribulation.  They will be judged according to their works.  Again, the image is one of temporal judgment, shame at the judgment seat, not eternal condemnation.  There is nothing in the language that suggests the salvation of the subjects is in question, or in danger.

Revelation  3:3

The church of Sardis

"the things thou has received and heard"  Nothing more is stated about the content of repentance.

The Lord shall return as a thief at an hour they know not (vs. 3)  The context is plainly related to the judgment seat of Christ, not eternal judgment.

Revelation 3:19

The subject called to repentance is "As many as [God] loves" (vs. 19).  The Greek word "phileo" requires that the call to repentance is direct to the believer.

The object of repentance is not plainly stated, and is inferred only from a poetic invitation.

The poetic language in both vs. 19 and 20 suggests that eternal rewards, and a more intimate fellowship in this age, are the consequences of repentance.