The last part of this verse stymies some translators.
The Young's Literal version reads:
"Trust in Jehovah, and do good, Dwell in the land, and enjoy faithfulness."
A loose translation bears out what we live on:
"Feed on Faith" or "Feed on His Faithfulness."
This translation represents the fullness of God's Word, and is fully consistent with the New Covenant:
"But he answered and said, It is written, Man shall not live by bread alone, but by every word that proceedeth out of the mouth of God." (Matthew 4: 4)
"In the beginning was the Word, and the Word was with God, and the Word was God." (John 1: 1)
"And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth." (John 1: 14)
We live by faith:
"For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith." (Romans 1: 17)
We live by Jesus' own faith:
"I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me." (Galatians 2: 20)
Jesus is the Living Word, and His Word now dwells in us:
"I have written unto you, fathers, because ye have known himthat is from the beginning. I have written unto you, young men, because ye are strong, and the word of God abideth in you, and ye have overcome the wicked one." (1 John 2: 14)
Now, how do we feed our faith? By hearing more about Jesus!
"Consequently, faith comes from hearing the message, and the message is heard through the word about Christ." (Romans 10: 17, NIV)
If we struggle to believe all the good things we have known about Jesus, the answer is to keep feeding on His Word!