When Jesus was born he was born into a Jewish family that kept the customs (ethos) of that religion and that family structure. Jesus was raised according to the laws, rules, and customs of Hebrews in his day.
41 Now his parents went to Jerusalem every year at the Feast of the Passover. 42 And when he was twelve years old, they went up according to custom. Luke 2:41-42 ESV
Now when it states that the family went to Jerusalem to celebrate the Passover that celebration was a custom of the family. It was a religious observance that Jesus as a child in that family was forced to follow. Maybe he liked that custom and maybe he hated some other customs but in reality he had no choice but to participate. This kind of custom (ethos) is in the name of religion. It is the kind of custom that one might identify with by being born in a Christian home or nation.
13 and they set up false witnesses who said, “This man never ceases to speak words against this holy place and the law, 14 for we have heard him say that this Jesus of Nazareth will destroy this place and will change the customs that Moses delivered to us.” Acts 6:13-14 ESV
Not following the religious customs will separate people and like Stephen, the first martyr, might even get one killed. The religious identity of the Pharisees was wrapped up in their customs.
Personal experience tells me that most youth when they leave home for college never return to the church they were raised in. I have even asked some high school teens directly if they had a choice would they be in Church each Sunday. I have also asked if they plan to continue to go to church after high school and the honest response from many is “no” to both questions. Some of those youth do find a church home wherever they live however many simply never return to any church. Even though they attended church as a youth it was never their custom (ethos). The feasts and celebrations might be kept because hey who does not enjoy a good holiday but the custom of actually attending a church or participating in some type of small group is not likely.
Jesus on the other hand became infused with the faith. God is real to him and he feels a call to ministry. After returning home briefly at the start of that ministry Luke writes that Jesus picked up in the home town synagogue right where he left off. Luke says that Jesus “as was his custom” (ethō) was in attendance at worship.
16 And he came to Nazareth, where he had been brought up. And as was his custom, he went to the synagogue on the Sabbath day, and he stood up to read. Luke 4:16 ESV
Jesus acted and participated. Jesus of his own desire and mind choose to be in worship reading scripture with others of like mind. Jesus was engaged. None could say Jesus was simply part of a religious custom (ethos) and ordinance required by his family, the religious leaders, or society. Participating in church had become the manner and custom (ethō) of his life. Jesus was living out a pattern of life that he had adopted, identified with, and had become accustom to living.
Now when they had passed through Amphipolis and Apollonia, they came to Thessalonica, where there was a synagogue of the Jews. 2 And Paul went in, as was his custom, and on three Sabbath days he reasoned with them from the Scriptures, Acts 17:2 ESV
In the same way Luke describes Paul as living a lifestyle of engaging with scripture before men. Paul’s life is engaged and in tune with the desires and service to God. Paul is not fulfilling a duty but he is living a life as is his custom.
One has several choices about how to engage in life and what things about life to make customary. Many people make the temporary pleasures of life their custom. But why? Because one can receive fleeting pleasure? Why not look eternally to see the example that Christ set and seek to make a relationship with God an integral part of daily life?
15 Do not love the world or the things in the world. If anyone loves the world, the love of the Father is not in him. 16 For all that is in the world—the desires of the flesh and the desires of the eyes and pride of life—is not from the Father but is from the world. 17 And the world is passing away along with its desires, but whoever does the will of God abides forever. 1 John 2:15-17 ESV