From today's first reading (1 John 2:29-3:6):
'My dear people, we are already the children of God
but what we are to be in the future has not yet been revealed;
all we know is, that when it is revealed
we shall be like him
because we shall see him as he really is.
Surely everyone who entertains this hope
must purify himself, must try to be as pure as Christ.'
For those who entertain the hope of eternal life with the Father in Heaven we
must purify ourselves and try to be as pure as Christ.
To purify ourselves means we live our lives with this order in mind: God first, others second, me third. If we live our lives in this way and, when we do wrong, we seek the forgiveness of God in the Sacrament of Reconciliation, then we are striving to be as pure as Chirst. This is what is asked of us: to be as pure as Christ. And, yes, it is a tall order. But it worked for the saints. They saints somehow managed to strive sufficiently hard to be as pure as Christ and to enter the Kingdom of Heaven. And this is the key: hard work. It's not an easy shift to be as pure as Christ and it isn't a case of simply being a 'good person'.
Yes, being a good person is a good start, assuming of course you are being a good person in accordance with God's commandments. But we must always strive to be more than just a good person. In being a 'good person' do we really put God and others first? Are we humble enough to not seek praise when we do good deeds? Do we, despite our good works, always believe we are not worthy to be in the presence of God in Heaven? You see, these are all qualities of the saints. They put everyone else first, they are incredibly humble, and yet despite all their great works and sacrifices, they still don't feel worthy to be in the presence of God.
That is the purity we must strive for. We will never be as pure as Christ, but we must try, and try very hard. Pray each and every day to Jesus and ask him to help you to become more holy. Ask him to open your heart up completely to the Holy Spirit so that the Spirit may work in you and assist you in your journey to become great; that is, great in the eyes of God, not in the eyes of the world.