The idea that “Jesus died for sinners” is a very hard one to swallow for Thai Buddhists because the idea of substitutionary atonement is absent from their religion. The Buddha taught that you are alone in the universe and that you must someday pay for your bad karma. No one can pay off your bad karma debt. You’re gonna get it eventually - either in this life or some successive life. Everything bad that happens to a person in their life is the result of some bad karma from their past. From this point of view, as you might imagine, Jesus dying on the cross looks a lot more like Jesus getting his just due for some bad karma in a previous life rather than the selfless sacrifice of the sinless Son of God.
Because the concept of substitution is largely absent from Buddhist thinking, there are a couple of illustrations from Thai history that I will often use to explain to people how Jesus could die on the cross, not for his own sin (which he didn’t have) but in order to save others. I take no credit discovering or coming up with either examples, but I have found them useful and hope that anyone else doing evangelism among Buddhists, particularly Thai Buddhists, might find them useful.
About four hundred years ago, when Ayuthaya was the capital of Thailand, Queen Suriyothai disguised herself as a warrior and followed her royal husband the king out to battle against the invading Burmese. In the battle, the Burmese king was just about to kill her husband when she deliberately drove her elephant between the two kings. The spear of the Burmese king, intended for the Thai king, pierced Queen Suriyothai instead. She saved her husband’s life, but she was killed. Suriyothai gave her life as a substitute for her royal husband. She died so he could live. Jesus Christ likewise died in the place of sinners so that they could live. A Thai gospel tract using this illustration is freely available online at Resources for Missions. Their was also an epic Thai movie about this story that came out in 2002 under the title “Suriyothai.”
Another example comes from Thai folklore. “Long ago, a king from the South besieged the king of Chiangmai in the North. Rather than see the city destroyed, the two kings agreed to select one man each for a contest to see who could stay under water the longest. The two men dived into the river. The first to emerge was the man from the South. Freedom for Chiangmai was assured. When the North’s man did not come up, the king sent men in to search for him. They found he had tied himself to a tree limb and so deliberately sacrificed his life for the city.” (Alex Smith, Buddhism Through Christian Eyes, OMF Publishers, Littleton, CO: OMF International, 2001, p.26 - NB. Smith's booklet has now been republished as "A Christian's Pocket Guide to Buddhism")