Our Obligation 
Yes, we who are reborn of the Holy Spirit have a loving obligation1 to be witnesses of the Truth so that others will have the opportunity of learning of it. 
This is done by our actions, our way of life and, by our words of life. Works and words. 
The following extract from the book "Names of Christ" by Moody Press served as the spark which started this off: 
The Faithful Witness.
Jesus Christ who is the faithful witness. (Revelation 1:5) 
This was the testimony of Christ Himself when He stood before Pilate (John 18:37): "To this end was I born, and for this cause came I into the world, that I should bear witness unto the truth. Everyone who is of the truth heareth my voice." This was His mission - to bear faithful witness. This is the obligation of every believer, "you shall be witnesses of me." This is the failure in a large measure of the church. The unsaved are waiting for the testimony by lip and life of professing Christians, and as they behold it, they are convicted by the Holy Spirit.
May the Holy Spirit Himself so control our lives that we shall count it our highest privilege to witness of Him before a sceptical world. Amen. 
The only way that we shall learn of what to do is by studying God's word under the supervision of the Holy Spirit who lives inside every reborn believer, and being lovingly obedient to our Lord's wishes. 
It is something that we shall choose to do. 
This has been more fully explained in a teaching of the parables of the pounds and the seeds of the sower, in the electronic book2 on this web site3
Blessed is every one that feareth the LORD; that walketh in his ways. For thou shalt eat the labour of thine hands: happy shalt thou be, and it shall be well with thee. 
(Psalms 128:1-2) 
I am the true vine, and my Father is the husbandman. Every branch in me that beareth not fruit he taketh away: and every branch that beareth fruit, he purgeth it, that it may bring forth more fruit. Now ye are clean through the word which I have spoken unto you. Abide in me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me. I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing. If a man abide not in me, he is cast forth as a branch, and is withered; and men gather them, and cast them into the fire, and they are burned. 
(John 15:1-6) 
1 Oblige: to bind morally or legally,  to constrain; to bind by some favour rendered, hence to do a favour to. 
Obligation: An act of obliging, a moral or legal bond, tie, or binding power, a debt of gratitude
2 Reflections.
3 www.hosanna.org.za