Intercession

A person who commits a Greater Sin and does not repent for it, is a transgressor. Namaz is not allowed behind him (he cannot lead a prayer assembly). His testimony is unacceptable. After death, he is liable for Divine punishment. By the Grace of Allah such a person may yet get salvation; and the Grace of Allah that can make this possible is the intercession of Muhammad (s.a.w.s.) and his Progeny (a.s.). 

As the Holy Prophet (s.a.w.s.) says in one of his traditions:
"My intercession has been kept for the sinful among my followers."
(Behaarul Anwaar vol.3). 

He (s.a.w.s.) also said,
"My intercession is specially for the sinful ones among my followers. But those who abstain from the Greater Sins, for them there is no accounting (of deeds)."

That is, they would be admitted to Paradise right away. 

Intercession Should not Prompt one to Commit Sins

There is hardly any doubt regarding the reality of Shafa'at (intercession). Actually it is the right bestowed upon the Holy Prophet (s.a.w.s.) and the purified Imams (a.s.), by Allah, to show their greatness and position. The other aim of intercession is to make their respect evident. The people who have committed Greater Sins shall be entrusted to them. By the grace of their intercession the sinful people will be able to ascend the heights like other groups of people. All this is evident from the Holy Qur'an and the authentic reports. It is also clear from Mutawatir (most frequently related) traditions. It would be needless to relate all such traditions for such a short discussion.

Only one point must be stressed at this stage. Intercession should not be taken as a license for committing sins nor should it make one heedless of repentance. 

Suicide in the Hope of Salvation

To sin and not to repent in the hope of intercession is akin to consuming poison or putting ones hand in the snake's mouth with the hope that a doctor would arrive and cure you. It is against logic, because after consuming poison it cannot be taken for granted that medical assistance would be available. Even if a doctor and medicines arrive on time it is still difficult to say that life would be saved. Before the medicine could have any effect the poison may spread to the whole body and death may occur.

In the same way, one who performs lewd actions in the hope that he would be interceded after death; cannot be sure that intercession will come to the rescue immediately.