Humans contribute nothing of their own to this salvation, since even believing (which the elect are indeed enabled to do) is a divine gift (cf. Rom 3:24–25). The key to this in the context of Eph 2:8 is what Paul had been driving home so forcefully up until now: Before God's gracious intervention believers were hopelessly dead, with their wills imprisoned by nature (φύσει, physei) in acts that led only to transgression and sin (2:1–5a, 12).
Ephesians, Evangelical Exegetical Commentary (Bellingham, WA: Lexham Press, 2015), 161.