Does repentance alone guarantee you salvation and eternal life?
Repentance is a complete change of ones
disposition. Repentance, Biblically speaking, effects the whole "character" of a person and is more than a simple change of mind. So if we are speaking of Genuine Repentance, as defined by Scripture, then the person repenting, has already experienced a work of Grace in their heart.
A person can repent for a lot of reasons. These are not Biblical Repentance:
1.) You are caught stealing a cookie and mom catches you - so you repent, in order to reduce her displeasure.
2.) Man is brought to justice and repents of his action before the judge - in hopes of a more lenient sentence.
3.) A plan goes seriously off the rails and you repent of ever having thought of it.
Biblical Repentance, will cause all to see the fruit thereof. This person will have a true change in their character. The Pharisees, of Matthew 3, who came down to John baptizing, were challenged by him because they had no fruit of Repentance.
Mat 3:7 But when he saw many of the Pharisees and Sadducees coming to his baptism, he said unto them, Ye offspring of vipers, who warned you to flee from the wrath to come?
Mat 3:8
Bring forth therefore fruit worthy of repentance:
There are Scriptures, that suggests that God, is the one who gives to us the spirit of Repentance.
Acts 5:31 Him did God exalt with his right hand to be a Prince and a Saviour,
to give repentance to Israel, and remission of sins.
Acts 11:18 And when they heard these things, they held their peace, and glorified God, saying,
Then to the Gentiles also hath God granted repentance unto life.
2Ti_2:25 in meekness correcting them that oppose themselves;
if peradventure God may give them repentance unto the knowledge of the truth,
If one believes, that God grants Repentance to His own, then Repentance, is the first fruit, of a person who is already saved. If one does not think, that God grants Repentance, then this Repentance may or may not be Genuine and only time will tell.