Except that official blindness upon Israel didn't stop Christ from preaching to them. John 12:36. The official blindness is then mentioned. 12:40. Yet then look at 12:42 "Nevetheless among the chief rulers also many believed on him;"
These never would have believed had Christ not first brought the message. Though He was aware of the offical blindness of Israel.
I will do my part, that God has given. I will trust Him to do His part.
Quantrill
It isn't my place to tell a fellow believer how to bear witness; if you feel called to cast the seeds broadly I wish you well with it.
Personally I feel that my efforts are best spent in a different manner. I've found that establishing a trust relationship with others and praying for them, then awaiting the moment when I feel that God is calling me to bear witness to someone I have come to know, someone who has recognized their own spiritual need and is open to hearing the word, is more effective for me. People are less inclined to dismiss and ignore a concerned friend who approaches them in a low-key and caring manner, in my experience, than someone they perceive as a "pushy stranger".
I'm always willing to discuss the gospel with someone who is interested; sometimes others stand nearby and listen even though they don't participate in the discussion, and you never know when or how your actions or words may bear fruit. Personally I don't feel comfortable pressing my witness on strangers, but we are not all called to serve in the exact same manner; some are called to preach, some to teach, some to simply let their life be an example. I think God uses each of us in the manner our talents are best suited for.
I have been privileged to be involved in the New Birth of a new believer, and it is always a wonderous and humbling thing to me as I recognize that in truth,
I did nothing;
He was the author of it, I was merely the pen he used to write with. I never fail to feel utter awe when I feel His hand at work in such things. To use a military analogy, He is the sniper, I merely happened to be the round that was in the chamber and the bullet that went downrange at His direction. I also never fail to feel unworthy of such a privilege, and humbly thankful that He saw fit to make use of me in this manner.
I recall times when I've talked until I was blue in the face at got nowhere.... then I would pray and ask Him to move, and sit back and wait.... and I'd get a phone call from the person, broken and crying and asking me what to do, and I'd know that He finally opened a path for the light to shine in. Then I get to watch faith take the place of doubt, hope take the place of despair, trust take the place of skepticism, and see someone's life turn around completely... it is awesome and all the miracle I need to see to strengthen my own faith.
I recognize that I cannot convert anyone; only God can. Therefore I humbly await my next turn to fly downrange, when He has spotted the next target and is ready to act. I am not the message, just the messenger, and that is an awesome privilege to me.
Anyway, that's just me... I do not presume to say how God may have called you to serve Him, but I am content with the part He has chosen me to play.