Is Titus 3:4-7 the best summary statement of the soteriology of the New Testament? I would say 'the theology of the NT' but it doesn't mention Gentile-inclusion. Yet if we're talking strictly soteriology, this seems to pretty much cover it all--
4 But when the goodness and loving kindness of God our Savior appeared, 5 he saved us, not because of works done by us in righteousness, but according to his own mercy, by the washing of regeneration and renewal of the Holy Spirit, 6 whom he poured out on us richly through Jesus Christ our Savior, 7 so that being justified by his grace we might become heirs according to the hope of eternal life.
And, stepping even further back, is there a better summary statement of what the whole Bible is about than Ephesians 1:7-10, particularly v. 10?
7 In him we have redemption through his blood, the forgiveness of our trespasses, according to the riches of his grace, 8 which he lavished upon us, in all wisdom and insight 9 making known to us the mystery of his will, according to his purpose, which he set forth in Christ 10 as a plan for the fullness of time, to unite [anakephalaiosasthai - to sum up, recapitulate, gather together, organically synthesize, bring under a single head/kephalos; see Rom 13:9!] all things in him, things in heaven and things on earth.