Preching means book distribution.
The sankirtana devotees are very very dear to Krishna. Because you are doing the field work of book distribution, Krishna has immediately recognised them as true servants. Just like during war time, a farm boy or ordinary clerk who goes to fight for this country on the front immediately becomes a national hero for his sincere effort. So Krishna immediately recognises a preacher of Krishna consciousness who takes all risks t deliver his message.
Lord Caitanya declares a war against Kali Yuga with "the bow" "the six Goswamis", by pulling back "the string" "Bhakti Vinod Thakur" making a thunderous sound, puts "the long strong arrow" "Bhakti Siddhanta Saraswati Thakur", having "the direction giving feather back of the arrow" "Sri Gaur Kishore Das Babaji Maharaj" and "the sharp penetrating arrow front" "Srila A.C.Bhakti Vedanta Swami Prabhupada".
The sufferings of humanity are due to forgetfulness of Krishna as the supreme enjoyer, the supreme proprietor and the supreme friend. Therefore, to act to revive this consciousness within the entire human society is the highest welfare work. One cannot be engaged in such first-class welfare work without being liberated.
A good dancer does not blame the stage! A good cook does not blame the utensils! A good engineer does not blame the instruments, so a good preacher does not blame the field of his preaching.