Does God approve of all things done in faith?

"...understand what the will of the Lord is..." – Ephesians 5:17

The Bible tells us that without faith, it is impossible to please God. Pleasing God requires that we do His will in faith. Does this mean that if we do practically anything as long as it is done in faith, we will please God?
Of course not.

Doing what God approves

I've seen people do "by faith" many things that weren't really pleasing to the Lord. God's Word tells us several things that He really hates, things that even if we do them "in faith," He would still be utterly displeased. For example:

In 1 Samuel 15, we read of how Saul's action displeased God. Samuel commanded Saul to destroy Amalek, but instead of utterly destroying everything in Amalek, Saul spared its king and its flocks because he wanted to "sacrifice to the Lord." While it might sound like an act of faith, it actually caused God to reject Saul as king of Israel.

In John 18:10-11, we read how Peter passionately defended the Lord Jesus by slashing off the right ear of Malchus. While we could assume that he merely did that to protect Jesus, he actually got rebuked for it.

God says He prefers for us to know Him than for us to merely offer something to Him (see Hosea 6:6). He wants us to know His heart and thus know what we should be doing. Only by knowing Him are we enabled to do what pleases Him.

God's will before our faith

We could go on with the many God-displeasing "acts of faith," but let's consider one last event in the Bible. In Matthew 16:21-23, we read how Jesus spoke to His disciples about His coming death and resurrection, and how Peter (again) rebuked Him for it.

"Far be it from You, Lord! This shall not happen to You," an impassioned Peter told the Lord Jesus, who responded with an answer we should all take note of:

"Get behind Me, Satan! You are an offense to Me, for you are not mindful of the things that are of God, but those that are of men."

The Lord Jesus' response to Peter is something that we must stand on. We can be passionate about many things, even bold in our faith, but if our faith and passion aren't for the things of God, the things that He wants, they're useless.

Be wise

Friends, the Bible urges us to be wise and to carefully determine what God's will really is (see Ephesians 5:15-17). Many Christians have been carried away by wrong teachings because they have not infused wisdom into their faith. Thus they failed to grow in the knowledge of Christ (2 Peter 3:18). They failed to know the heart of God according to His Word.

They might have faith, but they failed to establish it on the one true Foundation where we must be built on: God Himself. (see 1 Timothy 3:15)