A common Christian formula is Deo iuvante, literally "with God helping", more naturally rendered in English as "with God's help" or "if God helps". It signifies that the matter in question will only be completed successfully if God favors it and actively cooperates.
The phrase has a long history. Google Books returns about 65,000 hits total for deo juvante, deo iuvante, juvante deo, and iuvante deo. (Both spellings are equivalent, and the word order doesn't matter, though it's more common to put deo first.) In chronological order, here are some that seemed interesting.
The Last Pagans of Rome takes use of deo iuvante in letters around 400 A.D. as evidence that their authors had converted from paganism to Christianity.
The national motto of Monaco is Deo juvante. The phrase appears on the coat of arms of its ruling family, the Grimaldis. Apparently this dates to 1297, when François Grimaldi took control of the city by a ruse involving soldiers dressed as monks.
This odd book on freemasonry reports records of acceptance in Latin of a high masonic degree ("Supreme Master") in a long series starting in 1324 and ending in 1804, nearly all with deo juvante, e.g.:
Ego Arnaldus de Braque supremum magisterium deo juvante acceptum habeo anno domini 1340.
Around 1427, Thomas à Kempis wrote in The Imitation of Christ, book 1, ch. 13, "On resisting temptations":
Qui tantummodo exterius declinat, nec radicem evellit, parum proficiet, imo citius ad eum tentationes redient, et pejus sævient. Paulatim, et per patientiam cum longanimitate Deo juvante melius superabis, quam cum duritia et importunitate propria.
One who merely avoids [temptations] outwardly, not tearing out the root, will make little progress. Indeed, the temptations will return to him more quickly and rage worse than before. Little by little, through patience and long-suffering you will overcome them with God's help better than with harshness and your own crude ways.
This book reports seven Dutch cargo ships, built from 1925 to 2008, named Deo Juvante, as well as other ships with the comparable names Deo Favente ("God favoring"), Deo Volente ("God Willing"), Deo Confidentes ("Trusting in God"), Deo Gratias ("Thanks be to God"), Deo Data ("Given by [or to] God"), and Deo Duce ("With God as the leader").
Usage continues to the present day. A search on Twitter reveals one or two occurrences a month, sometimes stuck into sentences in other languages.