Am I my brother's keeper?

In Sunday school, we talked about the parable of the sower. The first seed was sown into rocky soil. The second seed was sown by the path and was trampled over....you know the story. The question of a person's motive for salvation was talked about and what is the best scenario for a person to come to Christ, yadda yadda yadda....anyway, what troubled me about that discussion is how responsible are we for a person's "walk" with Christ??? I believe that we are to be ambassadors for Christ and bringing people into a saving knowledge of Christ and, yes, there should be discipling process to get that person firmly rooted on good soil. Beyond those steps, are we to work out every person's salvation for them?? I don't think so!!!!
Doesn't God's word promise that he will make us new creatures??? Isn't it the role of the Holy Spirit to convict and protect???? If a believer chooses to be milk-fed and not be transformed, for whatever reason, that is thier sad choice and not God's plan for them. The parable talks about the circumstances surrounding the salvation experience lends itself to what kind of walk they will have. Aren't we called to plant seeds???? I think one could go mad wondering if the "seed" landed in the proper "soil" with the perfect ph-balance, you know what I mean???