I feel that the essence of spiritual practice is your attitude toward others. When you have a pure, sincere motivation, then you have right attitude toward others based on kindness, compassion, love and respect.
Material objects give rise to physical happiness, while spiritual development gives rise to mental happiness. Since we experience both physical and mental happiness, we need both material and spiritual development. This is why, for our own good and that of society we need to balance material progress with inner development.