BJP and Congress are the two most important political parties of India which have a pan India presence.
However, there are major ideological differences between both the parties and one has to understand the foundation of these parties to develop an understanding of the ideological differences among both these parties.
BJP or Bharatiya Janta Party emerged out of Bharatiya Jana Sangh in the year 1980. From a mere 2 seats in Lok Sabha in its earlier days, the party has grown emphatically and Narendra Modi was able to form a majority BJP government in the year 2014.
BJPs political ideology has been based on religion for a better part of its existence and it advocated the Ram Janambhoomi issue in its initial years. Later, however, it realized its folly and has shown a more secular face to the voters.

Congress which is also considered as an age-old party in India was formed in the year 1885 under the leadership of AO Hume. The party which has ruled India for most of the years has seen an ideological shift in its policies over the years and has borne the brunt of this move. Congress showcases it as a secular front and promises to take every citizen of India as a stakeholder in development.