Wealth is means for the man's welfare. In other words, wealth promotes welfare. For example, the consumption of goods like roti, milk, cloth, etc., all promote human welfare. In fact, an increase in the stock of wealth does not always promote human welfare. The welfare of the society or the nation depends upon the way in which wealth is produced. When wealth is produced under unhealthy conditions like long hours of work, risky jobs, unhygienic environment, etc., it adversely affects human welfare. This is what happened in England in the early phases of Industrial Revolution.
Further, welfare of the society or the nation also depends upon the distribution of wealth among the people. If the distribution of wealth is unequal, the social welfare may not increase. A large section of the society will be very poor and will lack the basic needs to have a comfortable life. Wealth of a nation does not, necessarily, ensure welfare of its people. On the other hand, if wealth is distributed equally, the welfare will be maximum. Lastly, if goods (or wealth) are produced to meet defence requirements such as guns, tanks, missiles, etc., they will not promote economic welfare. However, production of such goods increase our national income.
Economists, however, assume that when wealth increases, welfare increases too. Even if there is any negative side effect (for instance, social tension due to inequality of wealth distribution), this negative effect is unable to outweigh the positive beneficial effect. The net effect is that, welfare increases. Similarly, when wealth decreases, welfare is assumed to decrease.