At the beginning of the Sermon on the Mount, Jesus makes it clear who he is speaking to.
“Blessed are the poor in spirit, for theirs is the kingdom of heaven” Matthew 5:3
Before anything else is said, he explains what it is to be one of his followers. We need to realise we have nothing we can offer God to make us acceptable before him. Nothing about us, our pride, our righteousness, our works can justify us before God. Once we have acknowledged we are truly poor in spirit, true, deep, exceeding happiness is ours when we trust in Jesus Christ instead of ourselves.
Jesus then follows with another facet of what it is to follow him.
“Blessed are those who mourn, for they will be comforted.” Matthew 5:4
As our relationship with Christ develops, we become ever more concious of our sinfulness, indeed we mourn over our sinful state. Yet, because of what Christ has done for those who trust him, we are comforted that our sins have been dealt with. To have one’s sins wiped away is happiness indeed.