When a believer who is fully absorbed in the remembrance of God recites the praises of God, he is in fact in consonance with the entire Universe; all things in heaven and on the earth join him in chorus, albeit in silent language. But, God had so specially blessed David that the hills, mountains and birds used to audibly join him when he recited the praises of God. Similarly, God taught David (through angels) the skills to make use of iron. He developed the technique of melting and moulding iron to such an extent that he could make the very fine links of which chain mail is composed. The suits of armour made from this could be worn like ordinary clothes. At that time, this technique was unknown to the world. A believer can make great advances in the fields of industry and science. But, it is essential that he should direct this human progress towards peace and goodness. Whatever he accomplishes should be done with the realization that, finally, he has to appear before God and be answerable to Him.