What did Hashem mean when He instructed Yaakov to leave, and promised that He would be with him?
Rashi: As long as he remained attached to Lavan (whom Hashem described as Tamei), Hashem's Shechinah would not rest on him, and only after he returned to his father's land would it rest on him. 1
Seforno: He promised that He would guard him on the homeward journey. 2
Ha'amek Davar: After he returns, Hashem will be with him to guard him from Esav. Hashem had not promised to guard him from Lavan.
Oznayim la'Torah: Hashem was hinting that, when the Nochrim begin to eye us with an Ayin ha'Ra and to turn against us, it's time to leave.
Did Hashem tell Yaakov to return right after Lavan and his sons started to resent him, or some time after?
Malbim: Initially, Hashem wanted that Yaakov stay there, so all were pleased with him. Now Hashem wanted him to return, so Yaakov heard and saw the ill will of Lavan and his sons. 1
Perhaps "ki'Smol Shilshom" (31:5) literally contrasts today to one or two days ago, like in Shemos 5:7, Yehoshua 4:18 and Shmuel I 21:6. However, in Melachim II 13:5 it means 'like in the past.' (PF)
What is "ul'Moladtecha" to which Hashem told Yaakov to return?
Ha'amek Davar: It is to his way of serving Hashem through Torah and Avodah. He should return to his father's land, but not to his father's house (Esav was still angry).
QUESTIONS ON RASHI
Rashi writes: "'Return to your forefathers' land [and I shall be with you]' - [... Here, with Lavan], I cannot rest My presence upon you!" Why not explain simply, that Hashem was promising to protect Yaakov on the journey?
Gur Aryeh: If Hashem's promise was only for protection, this should have been stated explicitly (e.g. see Bereishis 28:15). "I will be with you" is all-inclusive. (Therefore, Rashi must explain why Hashem would not be with him here, in Charan.)
Rashi writes: 'Return to your forefathers' land' - [Only] there, shall I be with you...." Rashi interprets this as a general promise for Hashra'as ha'Shechinah. But later, Rashi (to 32:10) cites our verse as a promise for protection!
Gur Aryeh: Hashem's promise was worded generally, to be all-inclusive, including a promise for protection.
