Optimal specialization occurs at the production combination where the PPF is tangent to the TOT or, in the language of economics, where the opportunity cost of producing an addition S is equal to S's relative price on the world market. Moving from autarky to trade does not increase everyone's real income as was the case in the one-factor classical model. Rather, following SS, the real income of the abundant factor rises as the country moves from autarky to trade, and the real income of the scarce factor may rise or fall. Australia is land abundant. India is labor abundant.
Wheat is land intensive relative to textiles.
The SS theorem argues that movement from autarky to trade will benefit the abundant factor in each country. The scarce factor would receive a smaller share of national income, which makes it worse off certis paribus. The abundant factor benefits both ways, which is why it clearly wins. The scarce factor has a smaller share of the larger national income pie. Although it is worse off relative to the abundant factor, its real welfare could be better, worse, or the same as before trade depending upon how the two forces are balanced.