"Let me offer my respectful obeisances unto the tulasi tree, which can immediately vanquish volumes of sinful activities. Simply by seeing or touching this tree, one can become relieved from all distresses and diseases. Simply by offering obeisances to and pouring water on the tulasi tree, one can become freed from the fear of being sent to the court of Yamaraja.If someone sows a tulasi tree somewhere, certainly he becomes devoted to Lord Krishna. And when the tulasi leaves are offered in devotion at the lotus feet of Krishna, there is the full development of love of Godhead." (from the Skanda Purana, as quoted by Srila Rupa Gosvami)
Tulasi is glorified throughout the Puranas and Pancaratra: It was for the spiritual upliftment of the souls in the material world that Lord Visnu created tulasi as the ocean of milk was being churned. Tulasi is more dear to the Lord than Laksmi, for Tulasi-devi undertook extreme austerities and worshiped the Lord with love in order to have Him as her husband, and the Lord fulfilled her wish.
"There is no better recipient of charity than a vipra, no better gift than cows, no better tirtha than the Ganga, and no better leaf than a tulasi leaf. Whatever one can obtain by offering the Lord all types of flowers and leaves may be attained by simply offering Him one tulasi leaf. An offering of flowers made of gold, jewels, and pearls is not equal to an offering of tulasi leaves."
"By offering the Lord tulasi leaves, a devotee is released from sins accumulated for one koti (ten million) lifetimes. When a devotee offers tulasi to the Lord's head, all the devotees unmentionable and undetected sins are destroyed. By sprinkling the Lord's house with water using a tulasi leaf, one is freed from all great sins. A person who has tulasi leaves in his mouth or on his head or body when he dies is guaranteed not to suffer in hell."