The words βάρος and φορτίον are both translated ‘burden.' The difference between the two words is that with βάρος (from βαρύς, ‘heavy') the burden is always heavy and oppressive; whereas the idea in φορτίον (from φέρω ‘to carry') is that it has to be carried, as freight, baggage, &c., though it need not be heavy; as the burden was which the Jewish leaders laid on others, Matt. 23:4; Luke 11:46; or it may be light, as the Lord says, "My burden is light." Matt. 11:30.
In Gal. 6:2, 5 both words are employed: "Bear ye one another's burdens (βά.).... for every man shall bear his own burden (φο.)" We may and should in sympathy bear one another's troubles, and so on; but each one is responsible for his own ‘bundle:' he cannot transfer it to another.
Those who had labored for twelve hours complained of the burden (βάρος,) they had borne. Matt. 20:12. The word is employed also in 2 Cor. 4:17 for the "exceeding and eternal weight of glory" which the apostle looked forward to in contrast with "our light affliction."