We establish a connection between two settings of representation stability for the symmetric groups Sn over C. One is the symmetric monoidal category Rep(S∞) of algebraic representations of the infinite symmetric group S∞ = n Sn, related to the theory of FImodules. The other is the family of rigid symmetric monoidal Deligne categories Rep(St), t ∈ C, together with their abelian versions Rep ab (St), constructed by Comes and Ostrik.We show that for any t ∈ C the natural functor Rep(S∞) → Rep ab (St) is an exact symmetric faithful monoidal functor, and compute its action on the simple representations of S∞.Considering the highest weight structure on Rep ab (St), we show that the image of any object of Rep(S∞) has a filtration with standard objects in Rep ab (St).As a by-product of the proof, we give answers to the questions posed by P. Deligne concerning the cohomology of some complexes in the Deligne category Rep(St), and their specializations at non-negative integers n.