"Just" believe as if believing in Christ is insignificant? (John 3:15,16,18; Acts 10:43; 13:39; 16:31; Romans 1:16; 3:22-28; 4:5-6 etc..). Belief/faith is only as good as the OBJECT that we place it in and to say that believing in Christ for salvation is insufficient to save is to say that the OBJECT of our belief/faith (Jesus Christ and His finished work of redemption) is insufficient to save. To believe in Christ for salvation is to trust in Christ as the ALL-sufficient means of our salvation. Christ's finished work of redemption is sufficient and complete to save believers. No supplements needed.
Yes, Christ's finished work of salvation is in respect to His "work of faith", or labor of Love. The gift is faith previously having none other than the imagination of the sinful heart of natural man . God calls that "no faith" not little, none.