A famous song/poem by John Newton, the former slave-trader who repented when God opened his eyes to his evil sins, resulting in true conversion, and he is also the author of the even more famous “Amazing Grace”. This one is about growing and sanctification. As we grow in holiness, God makes us feel the deeper hidden evils in our prideful hearts. So that Christ becomes “our all” (our all satisfaction and sufficiency for every need) “Christ is all” (we need ultimately) and “Christ is in all” kinds of cultures, ethnicities, peoples, nations, social classes. Colossians 3:11.
Notice the last line, “that thou may’est find thy all in Me” = “in order than you may find your all (satisfaction, fulfillment, joy) in Me”
If you are in Christ, pray Colossians 1:9-14 regularly.