The beatitude describe people who have saving faith and will inherit a place in the kingdom of God. Upon conversion, we don’t start perfectly, courageously and consistently displaying all these qualities of poor in spirit, meek, mourning and so forth. Rather as we grow in faith, we grow in these qualities.
While Matthew 5:5 is probably the most famous beatitude, not many people understand what it means. Jesus does not explain what he means by “meek”, but he is quoting Psalm 37 which gives us a very big clue.