The inclusion of Directive Principles of State Policy in the Indian Constitution serves the main purpose of establishing a welfare state. These principles provide guidelines for the government to achieve the welfare and well-being of its citizens. Option 1 correctly identifies this purpose.

Option 2, which suggests the purpose is to establish a secular state, is not accurate. While secularism is an important aspect of the Indian Constitution, the Directive Principles specifically focus on addressing social and economic inequalities to ensure the welfare of the people.

Option 3, claiming the purpose is to check arbitrary action of the government, is partially correct. While the Directive Principles do provide a framework to limit arbitrary action, this is not their main purpose.

Option 4, stating the purpose is to provide best opportunities of development by the government, is not accurate. The Directive Principles aim to establish a welfare state rather than solely focusing on development opportunities.