The forerunner of the Cheka was the Military Revolutionary Committee (MRC). "Its duties were transferred" when the MRC was dissolved on Dec 5, 1917 (Orlando Figes, Revolutionary Russia, 1891-1991, Pelican (2014), p.134).

Via the MRC, the Bolsheviks had taken control of the Russian military garrison at Petrograd on Oct 21, 1917, after the provisional government's prime minister Alexander Kerensky made plans to move these soldiers to the Northern Front. More accurately, "the bulk of the soldiers... switched their allegiance to the MRC" and this constituted "the first act of uprising" (Figes, p.128).

Upon the Cheka's inception on Dec 7, 1917 its leader, Felix Dzerzhinsky, described the Cheka as the key to winning the civil war, on the "internal front":

We need to send to that front... determined, hard, dedicated comrades ready to do anything in defence of the Revolution. It is war now - face to face, a fight to the finish. Life or death.

The words 'Death to the bourgeoisie!' were displayed on the walls of the Cheka.

The failed attempt on Vladimir Lenin's life on Aug 30, 1918 prompted the beginning of the Red Terror in earnest - carried out formally by the Cheka. The Red Terror's significance (and by association the Cheka's) in consolidating Bolshevik Power was attested to by Leon Trotsky in Terrorism and Communism in 1920:*

Without the Red Terror, the Russian bourgeoisie, together with the world bourgeoisie, would throttle us long before the coming of the revolution in Europe.

Stalin and Lenin also supported the Red Terror as a means to win the civil war (Figes 158).

*available in print - 2007 edition, with commentary from Slavoj Žižek - and as a free e-book.

tl;dr The Cheka's forerunner, the MRC, oversaw the first act of Bolshevik uprising. The Cheka was founded with primary goal of fighting the civil war. So it was a vital component in taking power. Then the Cheka was also at the forefront of the Red Terror, which the Bolshevik leaders saw as the only way for the Revolution to survive.