When this question was posed to me last week, I didn't exactly know what to think because I had never considered it. But as I thought about it for a few minutes, I concluded that the flag should not be in the sanctuary.
My conclusion is far from being set in stone, but I have not seen a compelling reason to change my mind yet. Let me elaborate on my reasoning.
The sanctuary was set up by God to teach us His plan of salvation. Note these words from inspiration:
Yet important truths concerning the heavenly sanctuary and the great work there carried forward for man's redemption were to be taught by the earthly sanctuary and its services. {PP 357.2}
Thus in the work of Christ for our redemption, symbolized by the sanctuary service, "mercy and truth are met together; righteousness and peace have kissed each other." Psalm 85:10. {PP 349.2}
The great truths set forth by the types in the service of the sanctuary were brought to view, and faith grasped the central object of all that system--the Lamb of God, that was to take away the sin of the world. {Ed 47.2}
It is clear that the purpose of the sanctuary transcends national ties; God's salvation is for all of humanity. Everything in the sanctuary pointed to Christ and His work. Hence, there were no nationalistic aspects in the sanctuary that God designed.
Were there flags in the way God set up the Israelites when He took them out of Egypt? Yes, there were. Each tribe had its own flag. But we should note that those flags were never used in the sanctuary or its services. The closest thing to a flag in the sanctuary would be the veils, representing Christ (Hebrews 10:20).
When we go into the sanctuary, our main goal should be to worship God in spirit and in truth. There should be nothing that draws our attention away from God and His work.
True, Old Glory stands for the great sacrifices that have been made to keep us free. But in light of the supreme sacrifice made by God to set us free, its glory fades into insignificance.
Yes, we should honor the flag and the principles for which it stands, and the people who sacrificed to establish and protect those principles. But not in the sanctuary, where we honor the Infinite.
WDYT?