“He saved us, not on the basis of deeds which we have done in righteousness, but according to His mercy, by the washing of regeneration and renewing by the Holy Spirit.” (Titus 1:5)
The noun “regeneration” points to the act of entering new life, while “renewing” points to the qualitative nature of that new life.
“Renewal without regeneration is cosmetic; regeneration without renewal is spiritual infanticide.” (The Pastoral Epistles for Pastors, p.553)