Genèse 28:20

And Jakob vowed a vow, saying, If the Word of the Lord will be my Helper, and will keep me from shedding innocent blood, and from strange worship, and from impure converse, in this way that I am going; and will give me bread to eat, and raiment to wear,

IF (‘IM’) G-D WILL BE WITH ME. Rashi comments: “If He will keep for me these promises which He made to me.” The reason for the condition is lest the sin cause the abrogation of the promises. And so the Rabbis said in Bereshith Rabbah, “Rabbi Huna said in the name of Rabbi Acha, ‘And behold, I am with thee, and yet it is written, If G-d will be with me! However, from here you infer that there is no assurance to the righteous in this world.’”
In line with the simple meaning of Scripture it is further possible that the word im does not indicate a doubt in the matter, but such is the way of Scripture when referring to future events, such as: until ‘im asithi’ (I have done). And so also: ‘Ve’im’ there shall be the jubilee of the children of Israel. In all these cases it means if there will come a time when the condition is satisfied, then the deed will be fulfilled, that is to say, ve’im does not mean “if it occurs,” but rather “when it occurs.”

אם יהיה אלוקים עמדי, to remove from me all the pressures which I am under, pressures which prevent man from giving his attention to matters which should receive his attention, i.e. to G’d and what He expects from man. What troubled Yaakov was what our sages in Eyruvin 41 described as the three problems which are liable to unbalance someone’s mind as well as his relationship to his Creator. They are: gentiles, being involved personally in natural disasters, and excessive poverty.

ושמרני, from wicked gentiles who would force him to change his lifestyle;

ונתן לי לחם לאכול, so that I will not be forced to violate both my own integrity and that ordained for me by my Maker.

וידר, the vow Yaakov made at this point was a conditional one. The conditional nature did not mean that Yaakov doubted the promise G’d had made to him and G’d’s ability to fulfill it; rather he was afraid that just as all of G’d’s promises presume that the recipient remains worthy of them, so Yaakov was also afraid that some errors he might commit in the future, sinful conduct, would invalidate G’d promises. This is the only reason that he prefaced the vow with the words: “if G’d will be with me, etc.” He was afraid that if he would commit a sin or sins he might never see his father’s house again so that he would be unable to fulfill the vow he was about to make.

לחם לאכול ובגד ללבוש, he did not ask G’d for anything but the bare necessities of life. He did not need to ask for water as people find enough water to drink all over on earth.

אם יהיה אלוקים עמדי, “as surely as G–d will be with me;” the plain meaning of this verse is not that Yaakov spelled out a condition, but that he swore an oath to G–d.