Repentance leads to forgiveness, because repentance leads to baptism.
When the Bible speaks of repentance, it is not referring to what many think of: crying time at the altar, telling God you're sorry, confessing your sins, etc. Although such things are included in repentance, they are not the sum total of it. We should not divorce repentance from conversion, baptism, etc.
2 Corinthians 7:10-11 gives one of the most detailed but concise explanations of repentance. It is not merely a mental state or feeling, nor a "resolve" alone.
The alien sinner has not repented fully until they have not only renounced sin, and assented to the facts of the Gospel, but have also called upon His Name in Christian baptism and begun following the Lord as His disciple.
99 and a half won't do.