Why did God prohibit the physically defected, and what is the deeper spiritual meaning?"
I believe it is for the same reason that there were regulations about physical uncleannesses requirements for Israel and why, on the Day of Atonement, atonement was made not just for their trespasses but also for the physical uncleannesses of the people of Israel of whom Exodus 19:5-6 had previously refered to as a kingdom of priests and a holy nation:
16 Thus he shall make atonement for the Holy Place, because of the uncleannesses of the people of Israel and because of their transgressions, all their sins. And so he shall do for the tent of meeting, which dwells with them in the midst of their uncleannesses. Leviticus 16:16
The straightforward interpretation is that God demands not only moral perfection but also physical perfection in his priestly kingdom, in his presence.
Turns out this is actually fundamental to the logic of the Gospel, as Paul explains:
50 Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God; nor does corruption inherit incorruption.
-1 Corinthians 15:50
We cannot fully dwell, serve, and fulfill God's purpose for us in his presence, in his kingdom, if our bodies are compromised, which all of ours are. We must be made perfect. And so, Paul describes the victory that we have in Christ Jesus as the solution to this problem.
53 ...This perishable body must put on the imperishable, and this mortal body must put on immortality. 54 When the perishable puts on the imperishable, and the mortal puts on immortality, then shall come to pass the saying that is written:
“Death is swallowed up in victory.”
55 “O death, where is your victory?
O death, where is your sting?”
56 The sting of death is sin, and the power of sin is the law. 57 But thanks be to God, who gives us the victory through our Lord Jesus Christ. 1 Corinthians 15:53-57
Indeed, it is in this hope of the redemption of our bodies from this present corruption unto perfection for which we were saved:
23 And not only the creation, but we ourselves, who have the firstfruits of the Spirit, groan inwardly as we wait eagerly for adoption as sons, the redemption of our bodies. 24 For in this hope we were saved. Romans 8:23-24a
This is why Jesus himself, in order to become the source of salvation for us, after his suffering death, had to be made physically perfect:
7 In the days of his flesh, Jesus offered up prayers and supplications, with loud cries and tears, to him who was able to save him from death, and he was heard because of his reverence. 8 Although he was a son, he learned obedience through what he suffered. 9 And being made perfect, he became the source of eternal salvation to all who obey him, 10 being designated by God a high priest after the order of Melchizedek. Hebrews 5:7-10
So in conclusion:
The deeper spiritual meaning is that:
- We all must be not only morally but also physically perfect in order to fully dwell with God in his kingdom, serving him, and fulfilling his ultimate purpose for us.
And
- The ultimate representative of us (The High Priest) who will redeem us from all our moral and physical imperfections must first himself be perfect - not just morally but also physically.