not by … but by: The contrast is between human actions that might be thought to deserve salvation and God’s grace (see Galatians 2:16). Salvation is through faith in God’s mercy alone (Ephesians 2:8).
washing of new birth: See Ezekiel 16:9; John 3:1–15; Ephesians 5:26; Hebrews 10:22; 2 Peter 1:9.
and renewal by the Holy Spirit: This demonstrates a complete departure from the life of sin and death and a transfer into the life of purity (see also Romans 12:2; 2 Corinthians 5:17; Colossians 3:10).