Countries will be directly competing with each other for the sale of goods, which will drive the prices of goods down for the consumers. Lower prices means more goods for consumers, higher sales for producers, and a corresponding increase in employment to meet the new demand for goods. Jobs are made available to people in foreign countries where no jobs existed before free trade, increasing the countries' standards of living, while increasing the profits of domestic corporations. The resolution of these two seemingly plausible analyses requires a look at the businesses producing goods and the people consuming them in each country. This comparison makes sense if you think about valuable objects like gemstones.
Diamonds are more expensive than garnets because, among other reasons, they are more rare.
If diamonds were more abundant, they might be cheaper than garnets. Although a country that does not trade is forced to produce the blend of capital and labor-intensive goods its citizens require, the country open to free trade will find it profitable to concentrate on producing the goods that heavily require the factor input of its relative abundancy. For instance, the U.S. has a relatively high abundance of capital, and would thus find it profitable to produce and export capital-intensive goods, like agricultural products. Meanwhile, the relatively labor abundant Mexico would find it profitable to produce labor-intensive goods, like textiles. This increased demand for relatively abundant factor inputs increases the amount paid for these factors.