Simply put, humanly speaking, God never really rested. The Sabbath (Hebrew Shabbat or Shabbas) was made for people, and not vice versa, which Jesus made quite clear (see Mark 2:27 NAS). Careful exegesis and hermeneutics require that we become sensitive to expressions which describe human beings and the human condition, but which when applied to God are really anthropomorphisms (i.e., applying human characteristics, faculties, and attributes to God, such as having ears, eyes, hands, a nose, feet, and so much more.
Since God is an inexhaustible source of power, strength, stamina, and the general ability to work, He is never, nor could He ever be, exhausted, drained, spent, pooped, or in need of a time for "decompression." In verses such as Isaiah 43:24 and Malachi 2:17 we read, respectively,
"'Thou hast bought me no sweet cane with money, neither hast thou filled me with the fat of thy sacrifices: but thou hast made me to serve with thy sins, thou hast wearied me with thine iniquities.'"
"Ye have wearied the LORD with your words. Yet ye say , Wherein have we wearied him? When ye say, 'Every one that doeth evil is good in the sight of the LORD, and he delighteth in them'; or, 'Where is the God of judgment'?"
Other versions translate wearied as
Wearied and wore out are the only two expressions which hint at God being physically exhausted. They are thus anthropomorphisms. (All the others touch on something which is true of God but does not connote physical tiredness. If I were to place all the other expressions under a general rubric, that rubric would be God's patience. Whereas God's inexhaustible power is infinite, His patience is not. That may sound surprising, but God's patience cannot be infinite since it comes to an end, particularly in "the Day of the Lord.")
As for God's inexhaustibility, take, for example, His maintaining of the universe by the word of His power! Take His kingdom-building work among literally every people-group in the world, not to mention each person within that people group! Take His "management and administration" of what goes on in heaven, on earth, and in the first heaven, where the devil seems--but only seems--to reign supreme. (Actually, he is the "prince of the power of the air," according to Ephesians 2:2, and he leads the ongoing rebellion of the fallen angels, now called demons, in the heavenly places, or the first heaven; see Ephesians 6:12).
God created the Sabbath to be a day of rest for His image bearers. He also commanded the Hebrews to set aside the last day of the week (which for modern-day Jews begins at sundown on Friday and ends 40 minutes past sunset on Saturday) for worship, reflection, meditation, and praise, as well as for recharging their batteries for another new week. Most Christian denominations today call the Hebrews' last day of the week, "the first day of the week," probably because they believe Christ arose from the dead on a Sunday. Slowly, the name "the Lord's Day" became to Christians, Slowly, after the completion of the New Testament canon, the phrase the Lord's Day became analogous to the Tanakh's Sabbath.
God Himself is in no need of slumber or sleep (Psalm 121:3-4; 132:4), or R & R, or vacations. He never needs "alone time" to recharge His batteries, so to speak. He is at work 24/7/365, and of course for all eternity! In other words, His work will never be done.
Many Christians believe that in heaven, God both is and will be (and I say this reverently) the Chief Executive of all the activity that goes on in His and His Son's kingdom, both now and in the new heavens and the new earth (Revelation 21:1-2).
By the way, when the book of Hebrews says in chapter 4, verse 10,
"For the one who has entered His rest has himself also rested from his works, as God did from His,"
the writer does not mean God rested, humanly speaking (another anthropomorphism). Rather, God's rest refers to God's completion of His work of creation as laid out in Genesis 1 and 2, and not His ongoing work in maintaining His creation and being Lord over His kingdom-work in the universe. God, I suggest, will never again create what He created once. He will, however, re-create it.
By re-create I mean God will one day take what has been spoiled by sin, that which is subject to aging, decay, death, and a host of "natural" phenomena on earth which we call, ironically, "acts of God" (e.g., floods, hurricanes, earthquakes, tornadoes, monsoons, tsunamis, and so on), and make it new. Call it the "new and improved" heavens and earth. Call it a restoration of what once was (that is, until our first parents chose to disobey God) to what it was always meant to be "in the beginning" (Genesis 1:1). God will certainly need to make some adjustments to it, as the Apostle Peter described, as follows, in his second letter:
"But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up. . . . Looking for and hasting unto the coming of the day of God, wherein the heavens being on fire shall be dissolved, and the elements shall melt with fervent heat . . .."(3:10 and 12 KJV; cf. Genesis 1:31 and Revelation 21:10 NAS).