"For I desire mercy and not sacrifice, and the knowledge of God more than burnt offerings." [Hosea 6:6]
Piety is the quality of being religious or reverent. We typically think of it as a good thing ("He prays all the time; he's so pious.") but I want to consider for a moment that if piety in and of itself becomes our goal that it can lead us to sin.
Consider the Pharisees of the 1st century. They were devout and very religious, but their hearts were not in the right place. They were so obsessed with obedience to the Law of Moses and to their own traditions that they missed the whole point of the Law: love. Jesus taught in Matthew 22:36-40 that the greatest commandment is to love the Lord your God and to love your neighbor, and said "On these two commandments hang all the Law and the Prophets." (v. 40). The Law was built around love; for God and for fellow man. The Pharisees had missed that point and were so obsessed with religious devotion that they had lost their compassion. In Mark 3:1-6 when Jesus healed a lame man, the Pharisees were livid that He had healed on the Sabbath. They couldn't have cared less that Jesus helped someone who was in need.
In this way the pursuit of piety, or religious devotion, can be a temptation that leads us to sin. Let us not become so obsessed with obedience to God's word that we lose our love and compassion for others; for those lost in sin, for those who are in need, for those who hate us and have done us wrong. Like Jesus, our mission should be to seek and save the lost [Luke 19:10], not try to prove to God what good little Christians we are.