Titus 3:4-6
4 But after that the kindness and love of God our Saviour toward man appeared,
5 Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost;
6 Which he shed on us abundantly through Jesus Christ our Saviour;
The Evangelism Study Bible - Titus 3:5
3:5 "Not by works of righteousness": See Ephesians 2:8-9.
"Washing of regeneration": The image of water in Scripture often portrays the Holy Spirit (see John 4:10). Paul used it here to describe the work of the Holy Spirit imparting new life to believers at the moment of conversion.
Thomas Constable's Expository Notes on the Bible - Titus 3:4-5
3:4-5 The appearance that Paul referred to here was the sending of Jesus Christ to die for us: the Incarnation. That was the greatest revelation of God's "kindness" and "love for mankind." God took the initiative. God does not save people because they behave righteously ("on the basis of deeds") but because He is merciful (cf. Rom. 3:27-28; 4:4-5; Gal. 2:16-17; Eph. 2:5, 8: 2 Tim. 1:9). The salvation that He provides consists of "regeneration," which Paul connected here to the "washing" off of sin's filth (John 3:3-8; Rom. 6:4; Eph. 5:26: 1 Pet. 1:3, 23) and "renewing by the Holy Spirit" (2 Cor. 5:17). Paul did not mention human faith here because his emphasis was on God's grace in providing salvation.
In verse 5 "washing" could refer to conversion, and "renewing" to the coming of the Holy Spirit on the new believer. Another view is that "washing" could refer to water baptism, with "regeneration" and "renewing" describing what the Spirit does (saving, Spirit-baptism, filling, and sealing) in salvation. Still others see "washing" as symbolic of the Word of God (cf. Eph. 5:26: 1 Pet. 1:23). Probably "washing" is a metaphor for spiritual cleansing and/or Spirit-baptism rather than for water baptism, with the emphasis in the entire phrase "the washing of regeneration and renewing by the Holy Spirit" being on the Spirit's cleansing, regenerating work. Note the reference to the work that all three members of the Trinity accomplished in our salvation in these verses.