Λοιπόν, ἀδελφοί, ἐρωτῶμεν ὑμᾶς καὶ παρακαλοῦμεν ἐν κυρίῳ Ἰησοῦ, ἵνα καθὼς παρελάβετε παρ' ἡμῶν τὸ πῶς δεῖ ὑμᾶς περιπατεῖν καὶ ἀρέσκειν θεῷ, καθὼς καὶ περιπατεῖτε, ἵνα περισσεύητε μᾶλλον (1 Thessalonians 4:1 W-H Text of 1881).
From Robertson's Word Pictures: Finally (loipon). Accusative of general reference of loipo, as for the rest. It does not mean actual conclusion, but merely a colloquial expression pointing towards the end (Milligan) as in 2 Corinthians 13:11 ; 2 Timothy 4:8 . So to loipon in 2 Thessalonians 3:1 ; Philippians 3:1 ; Philippians 4:8 . We beseech (erwtwmen). Not "question" as in ancient Greek, but as often in N.T. ( 1 Thessalonians 5:12 ; 2 Thessalonians 2:1 ; Philippians 4:3 ) and also in papyri to make urgent request of one. How ye ought (to pw dei uma). Literally, explanatory articular indirect question (to pw) after parelabhte according to common classic idiom in Luke ( Luke 1:62 ; Luke 22:2 Luke 22:4 Luke 22:23 Luke 22:24 ) and Paul ( Romans 8:26 ). That ye abound (ina perisseuhte). Loose construction of the ina clause with present subjunctive after two subordinate clauses with kaqw (as, even as) to be connected with "beseech and exhort." More and more (mallon). Simply more, but added to same idea in perisseuhte.
George Milligan says the following about 1 Thess 4:1:
λοιπόν] a colloquial expression frequently used to point forward to a coming conclusion (cf. 2 Corinthians 13:11, 2 Timothy 4:8; τὸ λοιπ. 2 Thessalonians 3:1, Philippians 4:8), but in itself doing little more than mark the transition to a new subject as in late Gk. where it is practically equivalent to an emphatic οὖν: cf. Polyb. 1:15. 11 λοιπὸν ἀνάγκη συγχωρεῖν, τὰς ἀρχὰς καὶ τὰς ὑποθέσεις εἶναι φευδεῖς, Epict. Diss. 1:22. 15 ἄρχομαι λοιπὸν μισεῖν αὐτόν, and the other passages cited by Jannaris Exp. 5. 8. p. 429 f.: see also Schmid Attic. 3. p. 135. As showing its frequency as a connecting particle in the κοινή (cf. B.G.U. 1039, 8 (Byz.)), Wilcken remarks that it has passed over into Coptic in this sense (Archiv 3. p. 507). In mod. Gk. λοιπόν has displaced οὖν altogether.
In the present passage οὖν is retained in the text by WH. mg., Tischdf., Zimmer, Nestle. It might easily have dropped out after the -ον of λοιπόν: on the other hand the combination λοιπὸν οὖν is found nowhere else in the N.T., cf. however B.G.U. 1079, 6 ff. (a private letter—1./a.d.) λοιπὸν οὖν ἔλαβον παρὰ το(ῦ) ἄραβος τὴν ἐπιστολὴν καὶ ἀνέγνων καὶ ἐλυπήθην.