Before the coming of Jesus, no one could enter the presence of God except those appointed to the priesthood. Entering the presence of God resulted in death. But with the establishment of the priesthood of Aaron, the priest could enter the presence of God wearing special garments embroidered with pomegranates and decorated with bells, which signified their appointment and privilege and also prevented their death.
And you shall make the robe of the ephod all of blue. It shall have in it an opening for the head, with a woven binding around the opening, like the opening in a garment, that it may not be torn. On its' skirts you shall make pomegranates of blue and purple and scarlet stuff, around its skirts, with bells of gold between them, a golden bell and pomegranate, a golden bell and a pomegranate, round about on the skirts of the robe. And it shall be upon Aaron when he ministers, and its sound shall be heard when he goes into the holy place before the Lord, and when he comes out, lest he die.
With the advent of Jesus the Christ, He became our priest and we no longer need a priest to approach our God for us in the holy place.
And it was not without an oath. Those who formerly became priest took their office without an oath, but this one was addressed with an oath,
"The Lord has sworn and will not change his mind,
'Thou art a priest for ever.'"
This makes Jesus the surety of a better covenant.
The former priests were many in number, because they were prevented by death from continuing in office; but he holds his priesthood permanently, because he continues for ever. Consequently, he is able for all time to save those who draw near to God through him, since he always lives to make intercession of the them.
For it was fitting that we should have such a high priest, holy, blameless, unstained, separated from sinners, exalted above the heavens. He has no need, like those high priests, to offer sacrifices daily, first for his own sins and then for those of the people; he did this once for all when he offered up himself. Indeed, the law appoints men in the weakness as high priests, but the work of the oath, which came later than the law, appoints a Son who has been made perfect for ever.
Therefore, brethren, since we have confidence to enter the sanctuary by the blood of Jesus, by the new and living way which he opened for us through the curtain that is, through his flesh, and since we have a great priest over the house of God, let us draw near with a true heart in full assurance of faith, with our hearts sprinkled clean from an evil conscience and our bodies washed with pure water. Let us hold fast the confession of our hope without wavering, for he who promised is faithful;
The bells remind us of the eternal priesthood of Christ Jesus that allows us to know God personally.
In more recent times, bell have been used to announce births, deaths, marriages or other matters of great importance. They have been used to call people to church for worship. Bells can be a symbol of celebration at the birth of Christ.
Throughout history, shepherds have put bells on their flocks as a way of keeping track of them. The bells alert them to where the sheep are and help them find them when they are lost.
All we like sheep have gone astray;
we have turned every one to his own way
For you were straying like sheep, but have now returned to the Shepherd and Guardian of your souls.
1 Peter 2:25
Bells can remind us that Jesus is our Shepherd, that he knows us, guides us and guards us and searches us out when we are lost.
The Lord is my shepherd, I shall not want;
He makes me lie down in green pastures.
He leads me beside still waters;
he restores my soul.
He leads me in paths of righteousness
for his name's sake.
Even though I walk through the valley of the shadow of death (or the valley of deep darkness)
I fear no evil;
for you are with me;
your rod and your staff,
they comfort me.
You prepare a table before me
in the presence of my enemies;
you anoint my head with oil,
my cup overflows.
Surely goodness and mercy shall follow me
all the days of my life;
and I shall dwell in the house of the Lord for ever.