There are six books they sell in a series. Each book has a theme such as love or unity and they are entitled "Jewels from the words of 'Abdu'l-Baha"
There are four kinds of love. The first is the love that flows from God to man; it consists of the inexhaustible graces, the Divine effulgence and heavenly illumination. Through this love the world of being receives life. Through this love man is endowed with physical existence, untill, through the breath of the Holy Spirit - this same love - he receives eternal life and becomes the image of the Living God. This love is the origin of all the love in the world of creation
The second is the love that flows from man to God. This is faith, attraction to the Divine, enkindlement, progress, entrance into the Kingdom of God, receiving the Bounties of God, illumination with the lights of the Kingdom. This love is the origin of all philanthropy; this love causes the hearts of men to reflect the rays of the Sun of Reality.
The third is the love of God towards the Self or Identity of God. This is the transfiguration of His Beauty, the reflection of himself in the mirror of His Creation. This is the reality of love, the Ancient Love, the Eternal Love. Through one ray of this Love all other love exists.
The fourth is the love of man for man. The love which exists between the hearts of believers is prompted by the ideal of the unity of spirits. This love is attained through the knowledge of God, so that men see the Divine Love reflected in the heart. Each sees in the other the Beauty of God reflected in the soul, and finding this point of similarity, thy are attracted to one another in love. This love will make all men the waves of one sea, this love will make them all the stars of one heaven and the fruits of one tree. This love will bring the realization of true accord, the foundation of real unity.