This verse is really Part 1 of an instruction which concludes in verse 5 (“… each one should carry their own load.”).  A burden is a load which is too heavy and needs to be shared.  However, each of us should bear our own responsibilities, and not be lazy, expecting others to do our work for us.  Burdens are different: they may be physical, emotional, mental or spiritual; and we are not designed to carry them alone. The law of Christ is to love one another in such a way that the burden is shared (John 13:34).
 
Jesus set the pattern when He said, “Come to me, all you who are weary and burdened, and I will give you rest.  Take my yoke upon you and learn from me, for I am gentle and humble in heart, and you will find rest for your souls.  For my yoke is easy and my burden is light.” (Matthew 11:28-30).  After He washed the disciples’ feet He said, “I have set you an example that you should do as I have done for you.” (John 13:15).

Jesus showed that real love is found in practical, humble, sacrificial service – if we cannot do it for others we would not have done it for Him (Matthew 25:34-36).  Burden-sharing is not just for the benefit of the burdened - it also brings fellowship to the church and glory to the Lord Jesus, proving that we really are His disciples (John 13:35).
 
We need to learn to look out for the burdens which others carry (Philippians 2:3-4).  It is the perfect antidote to self-centred preoccupation with our own troubles.  Indeed you often find those who serve others most, are the people with the least resources.  Having seen the burden, we should be willing to be a burden-sharer, not just for a few minutes or even a day, but in a commitment to the Lord to be His servant to that person for as long as He commands.  Those who are burdened because they do not understand God’s way need to be taught from the Bible.  Those in grief need time and truth.  Those whose burden at work or home is impossible to bear need mercy and help.  Those with physical needs require a willing and skilful application of energy.  Those with a burden of sin need to be led to the Saviour.  So, be watchful, be discerning, be willing and be active in carrying each other’s burdens.