"That" is Jesus and His subsequent Millennial kingdom.....
Look at chapter 1 of the same book....
1 Corinthians 1King James Version (KJV)
1 Paul called to be an apostle of Jesus Christ through the will of God, and Sosthenes our brother,
2 Unto the church of God which is at Corinth, to them that are sanctified in Christ Jesus, called to be saints, with all that in every place call upon the name of Jesus Christ our Lord, both their's and our's:
3 Grace be unto you, and peace, from God our Father, and from the Lord Jesus Christ.
4 I thank my God always on your behalf, for the grace of God which is given you by Jesus Christ;
5 That in every thing ye are enriched by him, in all utterance, and in all knowledge;
6 Even as the testimony of Christ was confirmed in you:
7 So that ye come behind in no gift; waiting for the coming of our Lord Jesus Christ:
8 Who shall also confirm you unto the end, that ye may be blameless in the day of our Lord Jesus Christ.