Concerning the shadow of things to come, Jesus Christ fulfilled Passover, Unleaven Bread, First Fruits, and Pentecost the first time around, and we await his second coming. Some understand and teach that Jesus Christ will fulfill the remaining three Feasts of the LORD at his second coming, which would begin at the Feast of Trumpets. Trumpets is the only Feast which occurs on the day the moon is sighted after the new moon beginning the seventh month. Be watchful for ye know not the day or hour of your Lord's return. The day and hour that the moon is sighted to begin Trumpets is not known, which is why we watch for it. This year it is sometime around October 3,4th, or so I've read because I'm no astronomer. Look at this passage where Paul tells them that he doesn't need to write them concerning the time of his return because they, being children of the light, already know.
Now, brothers and sisters, about times and dates we do not need to write to you, 2 for you know very well that the day of the Lord will come like a thief in the night. 3 While people are saying, “Peace and safety,” destruction will come on them suddenly, as labor pains on a pregnant woman, and they will not escape.
4 But you, brothers and sisters, are not in darkness so that this day should surprise you like a thief. 5 You are all children of the light and children of the day. We do not belong to the night or to the darkness. 6 So then, let us not be like others, who are asleep, but let us be awake and sober. 7 For those who sleep, sleep at night, and those who get drunk, get drunk at night. 8 But since we belong to the day, let us be sober, putting on faith and love as a breastplate, and the hope of salvation as a helmet. 9 For God did not appoint us to suffer wrath but to receive salvation through our Lord Jesus Christ. 10
If the Christian Church isn't observing the Feasts of the LORD, how should they know the appointed time of Jesus's return and doesn't that mean they are in darkness? Parts of the law are still unfulfilled, and those parts tell us when Jesus is to return. Trumpets is a Sabbath also, but it falls on Monday or Tuesday this year. Sin is transgression of the law. How might Jesus react finding those professing his name to be profaning the Sabbath at his return? Might he say, "Depart from me ye who work lawlessness, I never knew you?"