SB 10.3.44

etad vāṁ darśitaṁ rūpaṁ
 prāg-janma-smaraṇāya me
nānyathā mad-bhavaṁ jñānaṁ
 martya-liṅgena jāyate
Synonyms: 
etat — this form of Viṣṇu; vām — unto both of you; darśitam — has been shown; rūpam — My form as the Supreme Personality of Godhead with four hands; prāk-janma — of My previous appearances; smaraṇāya — just to remind you; me — My; na — not; anyathā — otherwise; mat-bhavam — Viṣṇu’s appearance; jñānam — this transcendental knowledge; martya-liṅgena — by taking birth like a human child; jāyate — does arise.
Translation: 
I have shown you this form of Viṣṇu just to remind you of My previous births. Otherwise, if I appeared like an ordinary human child, you would not believe that the Supreme Personality of Godhead, Viṣṇu, has indeed appeared.
Purport: 

Devakī did not need to be reminded that the Supreme Personality of Godhead, Lord Viṣṇu, had appeared as her son; she already accepted this. Nonetheless, she was anxious, thinking that if her neighbors heard that Viṣṇu had appeared as her son, none of them would believe it. Therefore she wanted Lord Viṣṇu to transform Himself into a human child. On the other hand, the Supreme Lord was also anxious, thinking that if He appeared as an ordinary child, she would not believe that Lord Viṣṇu had appeared. Such are the dealings between devotees and the Lord. The Lord deals with His devotees exactly like a human being, but this does not mean that the Lord is one of the human beings, for this is the conclusion of nondevotees (avajānanti māṁ mūḍhā mānuṣīṁ tanum āśritam). Devotees know the Supreme Personality of Godhead under any circumstances. This is the difference between a devotee and a nondevotee. The Lord says, man-manā bhava mad-bhakto mad-yājī māṁ namaskuru: “Engage your mind always in thinking of Me, become My devotee, offer obeisances and worship Me.” A nondevotee cannot believe that simply by thinking of one person, one can achieve liberation from this material world and go back home, back to Godhead. But this is a fact. The Lord comes as a human being, and if one becomes attached to the Lord on the platform of loving service, one’s promotion to the transcendental world is assured.