Answer: To know Him, to love Him, and to serve Him in this life in order to be happy with Him forever in eternity.
Our primary obligation in life is to save our immortal souls by knowing, loving, and serving God. (Catechism) All else must take second place.
Every Catholic has an obligation to grow daily in his knowledge of God in order to more perfectly love and serve Him. It is impossible to serve God properly without knowing His holy Will. And we are obligated to serve God, for only thus do we prove our love for Him.
A Catholic must use every means available to him to grow in that knowledge, love, and service of God: Holy Mass, the Sacraments, prayer, spiritual reading, penance, etc.
An ideal means of fulfilling this obligation of every Catholic is: