Matthew 5:6 Blessed are those who hunger and thirst for righteousness, For they shall be filled.
The righteousness expressed here is not the doing and being good we normally associate with the word but the justifying righteousness of Christ alone.
We receive the from Christ through our faith, our believing in what we cannot see or fully understand; our simple belief.
To hunger and thirst after this gives us depth of our need for this righteousness and perception of how important it is to us.
God will fill us with this new righteousness in Him. The joy and peace that comes with it will stay with us as long as we choose to accept Him and stay with Him.