Ephesians 5:18-19 says, "And be not drunk with wine but be ye filled with the Spirit, Speaking to yourselves in psalms and hymns and spiritual songs, singing and making melody in your heart to the Lord;" This passage is speaking about our attitude. It tells us to be filled with the Spirit. We have the spirit indwelling us. But apparently, from this verse we have a choice as to whether or not the Spirit will fill us up. God commands us to allow the Spirit to fill us up.
The next verse is striking. God commands us in His word to sing in our heart. He says to sing psalms, spiritual songs, and hymns in our heart to the Lord. Are you doing that? Many times the average Christian will live walking around grumbling. They will focus on the cares of this life, and their schedule and busyness. Christians walk around humming songs of the world that, may not be bad, but their focus is not the Lord.
I would challenge you, sing a song to the Lord. Wherever you are. God wants you to sing to Him. God wants you to walk around singing and making melody to Him. Ah, now notice the phrase, "in your heart." I’m sure there are some people who would rather not like to listen to your singing, but God does, so sing to Him in your heart continually.
But then again, maybe you should just belt it out, ’cause Psalm 98:4 says,
"Make a joyful noise unto the LORD, all the earth: make a loud noise, and rejoice, and sing praise."