Rahu Ketu Dosha
The delay in marriage is usually attributed to some 'dosha' in the horoscope of the boy/girl to be married. Rahu - Kethu 'parihara' is considered as the main remedy for neutralizing the 'dosha'.
Rahu and Ketu are shadowy planets. Their movement is interrelated and as parts of one body they are at all times just opposite to each other but keeping in view of aspect (drishti), they can be regarded together. Both of them are considered together in the later houses.
For example, if Rahu is in the first house and Ketu is in the seventh house, in this case both will be supposed to be together in the seventh house (which is one of the later houses).
Node in House No. 1 to 6 will merge its effect into house No. 7-12 except house No. 5 & 11 where each node has its individual effect confined to that house only.
Rahu Dosha Remedies
In general, Rahu carries the positive and beneficial tone of Jupiter and hence stands for growth and development and self help while Ketu expresses the restrictions and obstacles of Saturn and hence thought to restrict growth.
In this way Rahu represents positive objectives and Ketu denotes the easy way out with little opportunity for growth. Thus Rahu signifies materialism and desires, whereas Ketu signifies spiritual tendencies and process of the refinement of materialization to spirit but obstacles in the material realm. Rahu is considered to be wile, deceitful and dishonest.
After all, Rahu did succeed in tricking Vishnu in serving him immortal nectar. Therefore, Rahu is described as a liar, foul mouth and full of criticism about others. He creates psychiatric disorders and other diseases of mind, especially when conjunct with Moon. However, if well placed in one's horoscope, Rahu gives courage, prestige and fame. It can bring out extraordinary qualities in terms of supernatural in an individual.
Ketu Dosha Remedies
Ketu is considered both malefic and benefic, as it causes sorrow and loss, and yet at the same time it turns the individual to God and the final liberation from the cycle of birth and death. Therefore, Ketu is an indicator of intelligence, wisdom, non-attachment, penetrating insight, derangement, and psychic abilities.
Despite of such negative characteristics, we survive with the wrath of these evil planets because they are bound to affect one or more houses in our horoscopes.