If you happen to be with an atheist who tells you that he does not believe in God, you can read him the whole library, where it says that God exists, and where it is proven that God exists, and he will not believe. [However] if in the presence of this same atheist you witness to a consistent, Christian life, something will begin to work in his heart…. It will be your witness that brings him the restlessness on which the Holy Spirit works.— Pope Francis: (Homily, Domus Sanctae Marthae, February 27, 2014)
Gospel Text: (MT 4:18-22)
As Jesus was walking by the Sea of Galilee, he saw two brothers,
Simon who is called Peter, and his brother Andrew,
casting a net into the sea; they were fishermen.
He said to them,
“Come after me, and I will make you fishers of men.”
At once they left their nets and followed him.
He walked along from there and saw two other brothers,
James, the son of Zebedee, and his brother John.
They were in a boat, with their father Zebedee, mending their nets.
He called them, and immediately they left their boat and their father
and followed him.
In today's Gospel reading, we see Jesus calling people into apostleship. Saint Andrew was the first Apostle (see John 1:40-42), and although he would later lead many others to Christ, the first person he evangelized was his brother, Simon (who later became Peter our first pope). Can you see the joy he shared with his brother?
Fulfilling our vocation of joy does not mean preaching conversion and debating the need to go to Mass. Consider every interaction with others as an opportunity for them to meet Jesus, even if they stubbornly refuse to recognize him in you.
They already know that you follow Christ and that you go to Mass because you believe that participation in church community makes an important difference, most especially receiving the Sacraments (Reconciliation & the Eucharist) regularly. You don't need to remind them of that with words. Simply concentrate on bringing more of Christ's joy into your day to day relationships. The Holy Spirit will take care of the rest!