Where did anyone get the idea that it was optional?
Certainly not from scripture!
Revelation 3:
[2] Be watchful, and strengthen the things which remain, that are ready to die: for I have not found thy works perfect before God.
[3] Remember therefore how thou hast received and heard, and hold fast, and repent. If therefore thou shalt not watch, I will come on thee as a thief, and thou shalt not know what hour I will come upon thee.
How does anyone miss this? - He told the Thessalonians that because they observed the times and seasons that Yeshua wouldn't come on them as a thief.
Don't we prefer to be Thessalonians? - The alternative is grim, as the above verse makes plain.
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Acts 1:
6 When they therefore were come together, they asked of him, saying, Lord, wilt thou at this time restore again the kingdom to Israel? 7 And he said unto them, It is not for you to know the times or the seasons, which the Father hath put in his own power. 8 But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.
Seems to me the Master gave some clear marching orders. Spread the Gospel.