In February Sielski fought in the Battle of Gołąb. In March Sielski met with the king in Lviv, and then accompanied him in a march to Warsaw, where he witnessed the surrender of Swedish Field Marshal Arvid Wittenberg. Arvid was imprisoned in Zamość where he later died in 1657. Sielski held the position of administrator of the treasury, tasked with raising funds to reorganize and pay the crown's army during the Battle of Warsaw.