The preceding verse (21:2) challenged my actions (“ways”) as opposed to my motives (“the heart”), because God knows and judges my heart. This verse points out that my actions (“do what is right and just”) counts more to the LORD than doing religious “sacrifices.”
“Sacrifice” in the Bible does not mean doing without something or giving something up. While there is an element of that, it actually refers to the religious act of bringing an offering to God at the temple and having it consumed on the altar.
This verse says it is “more acceptable to the LORD” that we live right every day than do religious stuff in His name. This is, in fact, a rather common theme in the Old Testament – even though sacrifices are still a priority (see 1 Sam 15:22-23; Prov 15:8; Isa 1:11; Hos 6:6; Micah 6:6-8).
But you say, “I thought God wanted us to go to church, give money, sing in the choir and teach Sunday School.” He does! Yet, He wants us doing the right things every day – for other people and in His name. That’s what gives power to all our church work!
Sadly, I’ve known men who would rather usher in church every time the doors are open than be a caring husband and father at home. God is not saying it isn’t good to serve at church, but He is saying what is “acceptable to the LORD” is our daily right choices. That’s what Matthew 5:23-24 and I John 4:20 are all about – our dealings with others (horizontal relationships) are priorities in our daily dealings with Him (vertical relationship)!