Bonaventure is more that just a theologian and Doctor of the Church. If we think of him as a Franciscan first, then we have to start with his commitment to poverty, his love of the natural world, and his opposition to rigid structures. Then we have to move into his mysticism which has a very practical side.
The natural world, Creation, is the first step towards God but it is not everything. Understanding starts in the world around us and flows upwards, toward God.
Blessed is the man whose help is from You. In his heart he is disposed to ascend by steps, in the vale of tears, in the place which he has set [Psalm, 84:6]. Since beatitude is nothing else than the fruition of the highest good, and the highest good is above us, none can be made blessed unless he ascend above himself, not by the ascent of his body but by that of his heart. But we cannot be raised above ourselves except by a higher power raising us up. But we cannot be raised above ourselves except by a higher power raising us up. For howsoever the interior steps are disposed, nothing is accomplished unless it is accompanied by divine aid. Divine help, however, comes to those who seek it from their hearts humbly and devoutly; and this means to sigh for it in this vale of tears, aided only by fervent prayer. Thus prayer is the mother and source of ascent in God.
-- From The Mind's Road to God 1,1