Or HaChaim on Genesis 14:19/אור החיים על בראשית י״ד:י״ט

1 ויברכהו ויאמר. He blessed him and said, etc. We need to understand whether the blessing which the Torah mentions here, i.e. ברוך אבדם, is the gist of the blessing. If that were so, why did the Torah have to introduce it with the words ויברכהו, "he blessed him?" I believe that the words ברוך אברם allude to an additional blessing. Were this not so, the expression ויברכהו should have been followed by the word לאמר.

2We must understand the matter as follows. First Malki Tzedek bestowed a blessing on Abraham which pertained to his personal wellbeing such as that his enemies should not be able to harm him, etc. Next he blessed him wishing him spiritual development a blessing directed to G'd who should allow Abraham to be His true servant. By being successful as a servant of the Lord, G'd Himself would be perceived by man as the owner of not only the heavens but also of the earth. He wished him that through him his descendants would acquire eternal life so that heaven and earth would endure forever. Our sages (compare Zohar 1,89) have expressed all this when they said that but for Abraham, G'd would not really have a true possession in either heaven or earth.

3Even the closing words of Malki Tzedeks' blessing, i.e. אשר מגן צריך בידך which ostensibly seems to be a blessing conferred by G'd on Abraham, are a blessing conferred upon G'd. G'd considers Himself blessed through the existence of a human being such as Abraham.