The red band worn on the left hand has many representations for a believer in Christ. First the colour bears significance to the blood that was shed for us by Jesus Christ on Calvary.
You may ask, why on the left hand? This is because we are a people positioned at the right hand of God. It signifies that God is holding our left hand with his right hand. Ps 138:7,139:10, 2 Sam 16:6The red band reminds us that we are a favoured people covenanted with God under the Abrahamic Covenant. From the bible Deut 7:6 tells us that God had chosen thee to be a special people unto himself, above all people that are upon the face of the earth (KJV)
The red band is brought to light in Gen 38:27-30 where a breach occurred and this thread was place on Zerah’s hand to signify first born but however Pharez broke forth and emerged first out of the womb. The word Zerah signifies rising or brightness; this is a representation that the true first born are to rise and inherit the double portion that is in store for them.