James Connolly was the only leader at the time who was into socialist causes - he was leader of a small group called the Irish Citizen Army. Connolly was talked into partaking in the Uprising which was planned by the Irish Brotherhood and the Irish Volunteers (Irish Volunteers military formed in 1913 which was in response to the Ulster Volunteers military in N Ireland - formed in 1912 - organized and paid for by the English government).
The socialists/communists/leninites/troskities... of today attempt (albeit successfully as you’ve just proved) to paint a picture that it was all about Connolly and his socialist revolution, and the Catholic Church was the boogey-man which couldn’t be further from the truth. Connolly was asked and did lead one of the factions but the planning etc was done by the IRB (Plunkett et al) and the Irish Volunteers. The Volunteers also included members of the Gaelic League, the Ancient Order of Hibernians, Sinn Féin, and secretly, the IRB.