7 To all who are in Rome, beloved of God and called to be saints: Grace to you and peace from God our Father and the Lord Jesus Christ. (Romans 1:7)
2 Unto the church of God which is at Corinth, to those who are sanctified in Christ Jesus, called to be saints, with all who in every place call upon the name of Jesus Christ our Lord, both theirs and ours: (1st Corinthians 1:2)
The calling of anyone who has been sanctified in Jesus Christ (through Holy Baptism) is obviously to become assimilated to God, by His Grace - so that all of their ways be Holy, as He is Holy.
13 Wherefore gird up the loins of your mind, be sober, and hope to the end for the grace that is to be brought unto you at the revelation of Jesus Christ;
14 as obedient children, not fashioning yourselves according to the former lusts in your ignorance:
15 but as he which hath called you is holy, so be ye holy in all manner of conversation;
16 because it is written, Be ye holy; for I am holy. (1st Peter 1:13-16)
If St.Paul speaks generally "of the Saints" in a sense sounding like he is speaking of the Church in general, he speaks in the sense of what each Christian's calling is, and of those who are obtaining to (or have already obtained to) great holiness.
Seraphim