Eschatology refers to the end of time. In Christian theology, time is linear, not circular. History will come to a definitive end. At that point, God will establish a New Jerusalem on earth where he will wipe all tears away.
When Gutierrez talks about eschatological promises, he is entering into an argument about where and how the Biblical end-time promises will be fulfilled. Some theologians contend that those promises will come to fruition only in the afterlife. We should simply forget about conditions getting better on earth, they say, and focus on our own salvation after death. The liberation theologists, including Gutierrez, strongly reject that concept, saying we humans are told to co-create with God a just society here on earth, within human history. For example, Jesus told Peter three times: "Feed my sheep."
Dietrich Bonhoeffer's theology was formed within the context of Nazi Germany and has had an enormous impact on liberation theologies around the world. He was a pastor in the Lutheran/Reformed Church when Hitler took power. Hitler almost immediately tried to remake the Protestant church in his own image, establishing a German Christian Church that excluded Jews (even those who had already converted) and other non-Aryans. Bonhoeffer immediately reacted. He opposed collaboration with the Nazis or any reinterpretation of the Bible. He believed very strongly that the Christian church had to actively and openly oppose Hitler. Most of his cohort, however, capitulated to the Nazis and, out of fear, went along with the new ideology. They buried their heads in the sand, falling back on the theology of the afterlife. They said there is nothing we can do about the conditions on this earth.
Bonhoeffer was deeply appalled and spent the last 12 years of his life, before the Nazis executed him, opposing this theology of withdrawal. He believed that God is both in heaven and, as the Jewish scriptures say, in the center of the village here on earth. We ought to be in the center of the village too, Bonhoeffer said, building God's kingdom here and now on earth.
When Bonhoeffer said freedom is acting on behalf of others, that sentiment came out of his recognition of his own privilege. He was a wealthy Aryan from a prominent family. He knew, for instance, that the Jews and other oppressed minorities could not speak up for themselves. Christians, Bonhoeffer said, have a central responsibility to stand up for the oppressed. Christians, he argued, must construct a "this-world" theology that focuses not on the afterlife or personal salvation, but on living here and now for other people.