Can We Know Now?
Jesus made it clear in John 3 that we must be born of the Spirit in order to be saved. This is the rebirth or becoming born again. This is not the baptism of the Holy Spirit according to most Christian beliefs including mine. Your beliefs, however, are the same beliefs that some Pentecostal groups have. That is how they come up with their beliefs that a person must speak in tongues in order to be saved. They confuse John 3 rebirth that Jesus described with the baptism of the Holy Spirit that the book of Acts describes. The works of the Holy Spirit are many. Some just cannot see that. The baptism of the Holy Spirit is for power according to the book of Acts. The rebirth of the Spirit is for our salvation and regeneration. At our rebirth we enter into a relationship with the Holy Spirit that we did not have before. He now becomes our helper, our teacher and our counselor as we seek Him and allow Him to be these things for us in our lives.
In the end of all this discussion on this thread the answer is yes, we can know for sure that we are saved while living here on earth.
Romans 8:16 King James Version
"The Spirit itself beareth witness with our spirit, that we are the children of God:"
In fact, the most important thing that we can do while living on earth is to make sure that our own salvation is sure. It can be done. For anyone who is not sure, please, please seek God in this matter so that you are sure. When the Spirit bears witness with your spirit, you will be sure. There will be no mistakes about it. Nothing will be worse than spending an eternity without God even if it means that you lose everything else that you have in life. That may mean the loss of friends, family or even financial security. To gain Christ is everything. All else is just dung anyway and only lasts for a brief time. Eternity is forever.