Malachi 1

You offer defiled food on My altar,
But say,
‘In what way have we defiled You?’
By saying,
‘The table of the Lord is contemptible.’
8 And when you offer the blind as a sacrifice,
Is it not evil?
And when you offer the lame and sick,
Is it not evil?
Offer it then to your governor!
Would he be pleased with you?
Would he accept you favorably?”
Says the Lord of hosts. vv.7-8

Read chapter 1
Religion vs. Relationship.  God knows the difference in our hearts in acts that are out of either of these two mindsets or rather "heartsets."
Malachi is a prophet to Israel after the captivity.  His name means "My Messenger."  We read of five different messengers in this short book of Malachi: Malachi, a true priest (2:7), John the Baptist (3:1), the Messiah (3:1-3), and Elijah (4:5).  We can see in all these messengers that the people killed the messenger because of the message which goes against the saying "don't shoot the messenger." 
The people of Israel are back in their land and starting new again in creating a living and following and upholding the law.  Yet the Lord sees that they have treated Him as a checklist, a have to, rather than a desire and want to.  There was no spirit of giving when they came to the altar of God for offering sacrifices, what they gave was their sick and lame of their flocks.  Their mindset was more of "killing two birds with one stone;" they would offer to the Lord to mark that off their good deeds checklist while at the same time getting rid of the weak to better their flock.  Yet they were not even thinking of God on the other end of these sacrifices.  He calls them out saying would they give that way to their governor, for of course they wouldn't wanting to please the men in that status.  They had fallen into religion and not relationship.  And this is still so true of believers today.  They've created a religion out of Christianity rather than a relationship with Jesus Christ.  It is not following certain rules that makes God pleased with us, He wants our hearts more than our sacrifices.  We ought to remember who's on the other side of this relationship and work to build that relationship as we would with our spouse or best friend because we love them and want to not because we have to or need to prove something to others.
Is your belief in God a religion or a relationship?  In what ways do you fall into a checklist of religion?  How do you build your relationship with Jesus?  May you seek Jesus and not a religion!