Deuteronomy 12:29-32
When the LORD thy God shall cut off the nations from before thee, whither thou goest to possess them, and thou succeedest them, and dwellest in their land; Take heed to thyself that thou be not snared by following them, after that they be destroyed from before thee; and that thou enquire not after their gods, saying, How did these nations serve their gods? even so will I do likewise.  Thou shalt not do so unto the LORD thy God: for every abomination to the LORD, which he hateth, have they done unto their gods; for even their sons and their daughters they have burnt in the fire to their gods.  What thing soever I command you, observe to do it: thou shalt not add thereto, nor diminish from it.

God had already showed Israel the way things were to be done.  He gave them guidelines for proper worship and the sacrifices and how they should relate to Him, what they should do and should not do.  But now when they enter the land, they will see the ways people worshiped their false gods, and God didn’t want his people getting any wrong ideas.  He was against those things that were being done.  They were not practices to be adopted by His people, but things to be destroyed.

God has given us His Word, His way, His path, the right things to do and the right way to live.  And we can’t look around and see what the world is doing and try to add those things in.  It’s not going to work, because those things are not pleasing to God.  Similarly, we can’t stop doing something that God said to do because it’s not the way of the world.  We can’t change anything about God’s established Word.  Our part is just to follow what He’s said.

God gave His people warnings about this because isn’t that really our temptation?  We see what other people do, and that puts ideas in our heads.  And we can think about it and compare it to what we are doing, and maybe we start to wonder why we aren’t doing it, too.  When we trust our own mind and our own heart, we can be led astray.  That’s why we need the anchor of the Word of God to show us what God says we are to do and not do.  We are to trust what He has to say about things.  We look to His example and His commands, not the world’s.

In this passage, the main thing God is talking about is worship.  As God, He gets to determine what is acceptable to Him.  And we cannot be so prideful to think we have better ideas about how things should work.  The main thing that got Israel into trouble was the way they approached worship.  When they were doing it God’s way, they prospered.  But as they started going astray from His guidelines in various ways, sometimes just small ways, they brought a lot of trouble upon themselves.  Jesus said that God seeks those who will worship Him in spirit and in truth, and the only way we can do that is by submitting to God’s Spirit and God’s truth and trusting that as the sole basis for what we do.