Because Russia is landlocked, he attempted to moderinze by establising trade. The Baltic and Black Sea were controlled by Sweden and the Ottoman Empire, respectively, and to acquire the abililty to trade through these areas he went to war with both.
One of his goals was to give Russia greater access to seas in the western part of his empire. He realized that naval power was increasingly important, and he also realized that Russia in the west had far less access to the sea than was true of such other powers as France, Spain, and England.
To modernize Russia, he also needed to unite them, and Peter the Great saw no way to do this but through force. He used an iron fist to bring the Church to heel, and ruthlessly dealt with opposition. He secured the outskirts of the empire and made attempts to modernize his army as well. As a symbol of the new Russia, he had St. Petersburg constructed on the Neva River.
Peter's major goal was to modernize and Westernize his country. He felt that Russia was an extremely backwards place that would be unable to be a power in the world unless it modernized. Therefore, a major goal of his was to modernize in order to become more powerful.