I believe this particular song speaks
about the goodness of our God. Because of that fact, I believe it is a praise song.
When we praise the Lord, in my opinion, we speak well
of Him and not just speak well
to Him.
This song, I believe, takes it lyric (at the least this one line) from Deu 28:3. But, take a look at this verse in context with verses 1 & 2.
Deuteronomy 28 (KJV)
1 And it shall come to pass, if thou shalt hearken diligently unto the voice of the LORD thy God, to observe and to do all his commandments which I command thee this day, that the LORD thy God will set thee on high above all nations of the earth:
2 And all these blessings shall come on thee, and overtake thee, if thou shalt hearken unto the voice of the LORD thy God. Now, because of these verses (which are a continuation of commands and instructions given by the Lord to Moses to give to God's people) we can say, 'We're blessed in the city, blessed in the fields' as it says in Deu 28:3.
I'll stop there concerning the song.
As for the remainder of your post, I'd say that the heart alone, being a deceitful thing as the Bible tells us, is not enough. There has to be some action that springs forth because of that which is in one's heart. As the Bible states, in Proverbs 23:6 & 7:
Proverbs 23 (KJV)
6 Eat thou not the bread of him that hath an evil eye, neither desire thou his dainty meats:
7 For as he thinketh in his heart, so is he: Eat and drink, saith he to thee; but his heart is not with thee.
See that, his heart is not with thee. To me, that says one's heart isn't even enough and in some cases, the actions that appear to be godly, aren't anywhere close. BTJM.
Be Blessed.