The "ifs and thens" of fasting and Shabbat...

Isa 58:5 “Is it a fast that I have chosen, a day for a man to afflict his being? Is it to bow down his head like a bulrush, and to spread out sackcloth and ashes? Do you call this a fast, and an acceptable day to יהוה?

Isa 58:6 “Is this not the fast that I have chosen: to loosen the tight cords of wrongness, to undo the bands of the yoke, to exempt the oppressed, and to break off every yoke?

Isa 58:7 “Is it not to share your bread with the hungry, and that you bring to your house the poor who are cast out; when you see the naked, and cover him, and not hide yourself from your own flesh?

Isa 58:8 “Then your light would break forth like the morning, your healing spring forth speedily. And your righteousness shall go before you, the esteem of יהוה would be your rear guard. (KJV says your "RE-REWARD" meaning something taken away would be given back! HalleluYAH!)

Isa 58:9 “Then, when you call, יהוה would answer; when you cry, He would say, ‘Here I am.’ “If you take away the yoke from your midst, the pointing of the finger, and the speaking of unrighteousness,

Isa 58:10 if you extend your being to the hungry and satisfy the afflicted being, then your light shall dawn in the darkness, and your darkness be as noon.

Isa 58:11 “Then יהוה would guide you continually, and satisfy your being in drought, and strengthen your bones. And you shall be like a watered garden, and like a spring of water, whose waters do not fail.

Isa 58:12 “And those from among you shall build the old waste places. You shall raise up the foundations of many generations. And you would be called the Repairer of the Breach, the Restorer of Streets to Dwell In.

Isa 58:13 “If you do turn back your foot from the Sabbath, from doing your pleasure on My set-apart day, and shall call the Sabbath ‘a delight,’ the set-apart day of יהוה ‘esteemed,’ and shall esteem it, not doing your own ways, nor finding your own pleasure, nor speaking your own words,

Isa 58:14 then you shall delight yourself in יהוה. And I shall cause you to ride on the heights of the earth, and feed you with the inheritance of Yaaqoḇ your father. For the mouth of יהוה has spoken!”

H6684

צוּם tsûm tsoom A primitive root; to cover over (the mouth), that is, to fast: -  X at all, fast.