reasons:

1. experience of my own and other lifes that have been changed positively. Prayers answered

2. the Jewish tora and other jewish books (also referred to as the old testament in the bible) which were written between 1500-500 BC speak about Jesus. There are numerous prophesies, analogies and a lot of symbolism that point to Jesus. It just shows that God had the whole plan of salvation laid out from the beginning.

3. life itself and the uniqueness of the earth in the whole cosmos. It is very unlikely that there is another planet out there with all its attributes that make life as we know it possible.