The 'hidden life' is a that of (1) seeking (Col 3:1-4); (2) laying aside sin (Col 3:5-9); and (3) putting on Jesus Christ -- His mind; character; and conduct (Col 3:10-17; Rom 13:14). 9 things about hidden life: (1) faith (Gal 2:20; 2Co 5:7); (2) only God sees our inner man (Jer 17:9-10; Heb 4:12-13; 1Pe 3:4); (3) 'in but not of the world' (1Jo 3:1); (4) God looks at the heart (1Sa 16:7); (5) the real 'you' will be revealed (1Co 4:5; 1Co 3:10-15); (6) Christ in glory leaves only the part of us compatible (Col 3:4; Rev 4:1-14); (7) glory or shame (1Jo 2:28); (8) nothing hidden that won't be revealed (Mar 4:22); (9) hidden things because of either shame or value will be revealed (2Co 4:2; 2Co 12:1-21; Mat 13:44).'
Paul never met the Colossians but wrote to them from a Roman prison around 62 AD to counter misconceptions of his day. It magnifies the character of Jesus Christ more than any other book in the New Testament, and counters misconceptions of our day as well. The key verse may well be Col 1:18 "...that in all things, He might have preeminence."