KJV below (Link to NIV)
9 Therewith bless we God, even the Father; and therewith curse we men, which are made after the similitude of God.
10 Out of the same mouth proceedeth blessing and cursing. My brethren, these things ought not so to be.
11 Doth a fountain send forth at the same place sweet water and bitter?
12 Can the fig tree, my brethren, bear olive berries? either a vine, figs? so can no fountain both yield salt water and fresh.
The point here is simple. It not only seems out of place for us to praise God after speaking ill or gossiping about someone else, particularly given that they are made in God’s image, it is impossible. Salt water and fresh water are incompatible. They can’t occur together. We need God to purify our mouths in order to praise him. He turned bitter water sweet in the dessert for the Hebrews and it is only by God’s help that we can worship Him as we should.
How often have you been running late for a “worship service” and found yourself yelling at the kids, or angrily spewing vitriol at a car in traffic? Jesus said his worshipers must worship God in “spirit and in truth.” We often think that we offer something to God in our worship, but how often do we consider that we are only able to worship God because of who God is?