Can a Christian's worship be hindered if they are in sin? Does God expect Christians to be completely holy when we worship Him?
"Husbands, likewise, dwell with them with understanding, giving honor to the wife, as to the weaker vessel, and as being heirs together of the grace of life, that your prayers may not be hindered" (I Peter 3:7).
"You ask and do not receive, because you ask amiss, that you may spend it on your pleasures" (James 4:3).
"Now we know that God does not hear sinners; but if anyone is a worshiper of God and does His will, He hears him" (John 9:31).
"There they cry out, but He does not answer, because of the pride of evil men. Surely God will not listen to empty talk, nor will the Almighty regard it" (Job 35:12-13).
"They cried out, but there was none to save; even to the LORD, but He did not answer them" (Psalms 18:41).
"If I regard iniquity in my heart, the Lord will not hear" (Psalms 66:18).
"When he is judged, let him be found guilty, and let his prayer become sin" (Psalms 109:7).
"The LORD is far from the wicked, but He hears the prayer of the righteous" (Proverbs 15:29).
"One who turns away his ear from hearing the law, even his prayer is an abomination" (Proverbs 28:9).
"The LORD is near to all who call upon Him, to all who call upon Him in truth. He will fulfill the desire of those who fear Him; He also will hear their cry and save them. The LORD preserves all who love Him, but all the wicked He will destroy" (Psalms 145:18-20).
"When you spread out your hands, I will hide My eyes from you; even though you make many prayers, I will not hear. Your hands are full of blood. Wash yourselves, make yourselves clean; put away the evil of your doings from before My eyes. Cease to do evil, learn to do good; seek justice, rebuke the oppressor; defend the fatherless, plead for the widow" (Isaiah 1:15-17).
"Behold, the LORD'S hand is not shortened, that it cannot save; nor His ear heavy, that it cannot hear. But your iniquities have separated you from your God; and your sins have hidden His face from you, so that He will not hear" (Isaiah 59:1-2).
"Therefore thus says the LORD: "Behold, I will surely bring calamity on them which they will not be able to escape; and though they cry out to Me, I will not listen to them"" (Jeremiah 11:11).
"Thus says the LORD to this people: "Thus they have loved to wander; They have not restrained their feet. Therefore the LORD does not accept them; He will remember their iniquity now, And punish their sins." Then the LORD said to me, "Do not pray for this people, for their good. When they fast, I will not hear their cry; and when they offer burnt offering and grain offering, I will not accept them. But I will consume them by the sword, by the famine, and by the pestilence"" (Jeremiah 14:10-12).
"Therefore I also will act in fury. My eye will not spare nor will I have pity; and though they cry in My ears with a loud voice, I will not hear them" (Ezekiel 8:18).
"Then they will cry to the LORD, but He will not hear them; He will even hide His face from them at that time, because they have been evil in their deeds" (Micah 3:4).
""Therefore it happened, that just as He proclaimed and they would not hear, so they called out and I would not listen," says the LORD of hosts" (Zechariah 7:13).
If you mean by "completely holy" that people must be sinless to approach the Lord of Glory, then no one could worship God. It is those who believe that they can remain in sin and still have God's favor who are mistaken. We are called to be a holy people, "Therefore gird up the loins of your mind, be sober, and rest your hope fully upon the grace that is to be brought to you at the revelation of Jesus Christ; as obedient children, not conforming yourselves to the former lusts, as in your ignorance; but as He who called you is holy, you also be holy in all your conduct, because it is written, "Be holy, for I am holy"" (I Peter 1:13-16). Sin might encroach on a Christian's life, but the Christian rejects it because his aim is to live pleasing to God. "What shall we say then? Shall we continue in sin that grace may abound? Certainly not! How shall we who died to sin live any longer in it?" (Romans 6:1-2).