Everything is Kṛṣṇa's energy. Kṛṣṇa is spiritual, so His energy is also spiritual. But in the spiritual energy there is the possibility of forgetting Kṛṣṇa. That is called material energy. So if we remember Kṛṣṇa, that is not material energy. A man, stone, wood, brick and constructs a big, high skyscraper building; that is material energy. But the same stone, same wood, same cement, you construct a very nice temple of Kṛṣṇa, that is spiritual energy. Now, the question is how the woods and stones which is matter, becomes spiritual. Is not that the question? We say one man is constructing big skyscraper building with woods and stones, we say this is materialism. But they can also challenge you that "You are also interested in woods and stones and constructing a big church or temple. Why is your idea spiritualism?" Now, you can compare. This is spiritualism means in this stone and earth and woods you remember Kṛṣṇa, "I am constructing something for Kṛṣṇa." Therefore it is spiritualism.
So the conclusion is when we forget Kṛṣṇa, that is materialism. And when we constantly remember Kṛṣṇa, that is spiritualism. The materialists means they are thinking of sense gratification. All these big, big buildings were constructed in your country, Edinburgh. The idea was that "We shall show something opulent that we are very great nation. We have got nice buildings, nice churches, nice roads." Puffed up. Everyone wants to be puffed up before his friends and relatives. So this is materialism. But the same thing done for the satisfaction of Kṛṣṇa, that "We shall construct this temple for Kṛṣṇa's inhabitation. We shall construct this building for providing the devotees of Kṛṣṇa so that they may be able to chant Hare Kṛṣṇa mahā-mantra without any disturbance..." It appears the same thing, karma and bhakti, but bhakti is always in relation with Kṛṣṇa and karma is always in relation with sense gratification. Therefore, the things, the ingredients is originally spiritual because it is Kṛṣṇa's energy. But ahaṁ mameti [SB 5.5.8], when we try to impose our proprietorship, that is materialism. Materialism means forgetfulness of Kṛṣṇa. Otherwise, there is no materialism; everything is spiritual. Hm. Then?
Prabhupada's lecture - Śrīmad-Bhāgavatam 1.2.5 - Edinburgh, July 17, 1972