Hi, Atemi.
This is a good question.
There is no obligation for any days in Scripture, so that comes from tradition that came long after the Apostles passed on.
However, we might be obligated to “keep the Lord’s day holy”. So, I suppose this commandment is a good bases for holy days of obligation.
Because that is what the Scriptures say the early believers did.
So, the scriptures do say that “believers” assembled but were not obligated (if you leave out the commandment part to “keep the Lord’s day holy”).
Meeting with the Body on Sunday is Scriptural, as is meeting other days of the week too.
Ok.
An obligation, at threat of grave sin, to meet on Sunday is tradition and is not found in God’s Word. We meet out of love of communal worship, not obligation.
I think if you deliberately do not “keep the Lord’s day holy”, would be a grave sin. Maybe the Church is on to something here. If they tell us that we are obligated to go to Church/Mass and we are obedient, we keep Gods’ commandments. I guess she’s just looking after her children like any responsible mom would.
I suppose the next argument would be to dispute that holy days of obligation are tantamount to “keeping the Lord’s day holy”. I’m easily convinced that going to Church/Mass on Sunday is an obligation base on the third commandment (i.e., Scripture). But we also know that the Church obligates us to go to Church/Mass on other days besides Sunday. These other days of obligation are:
January 1, the solemnity of Mary, Mother of God;
Thursday of the Sixth Week of Easter, the solemnity of the Ascension;
August 15, the solemnity of the Assumption of the Blessed Virgin Mary;
November 1, the solemnity of All Saints;
December 8, the solemnity of the Immaculate Conception;
December 25, the solemnity of the Nativity of Our Lord Jesus Christ.
I honestly don’t know if there are any Scriptural bases for Church/Mass attendance obligation on these other days besides Sunday. However, I can certainly understand why these days are important.
BTW, I think if you love the Lord, it really doesn’t feel like and obligation anyway.
God bless…